(en)The invention relates to novel enzymes that provide acetylated sphingoid bases.

1.ApplicationNumber: US-201314391480-A
1.PublishNumber: US-2015118721-A1
2.Date Publish: 20150430
3.Inventor: SCHAFFER STEFFEN
FARWICK MIKE
ANDREA HEIKO
KOEHLER TIM
WOLFF DANIEL
TER VELD FRANK
POETSCH ANSGAR
BOLES ECKHARD
SCHORSCH CHRISTOPH

4.Inventor Harmonized: SCHAFFER STEFFEN(DE)
FARWICK MIKE(DE)
ANDREA HEIKO(DE)
KOEHLER TIM(DE)
WOLFF DANIEL(DE)
TER VELD FRANK(DE)
POETSCH ANSGAR(DE)
BOLES ECKHARD(DE)
SCHORSCH CHRISTOPH(DE)

5.Country: US
6.Claims:
(en)The invention relates to novel enzymes that provide acetylated sphingoid bases.

7.Description:
(en)FIELD OF INVENTION
Novel enzymes which provide acetylated sphingoid bases are the subject of the invention.
PRIOR ART
Pichia ciferrii has already been used since the start of the 60s for the production of sphingoid bases and sphingolipids.
The yields of sphingoid bases and sphingolipids from wild type strains are always open to improvement.
Sphingoid bases, in particular phytosphingosine, sphingosine and sphinganine, are used in diverse ways as cosmetic active substances for protection and care of the skin.
They are incorporated into cosmetic care products either directly or after chemical conversion to skin-identical ceramides.
The non-conventional yeast Pichia ciferrii is characterized in that it secretes relatively large quantities of acetylated sphingoid bases, mainly tetraacetylphytosphingosine (TAPS) and triacetylsphinganine (TriASa), into the culture medium. The TAPS formed can be extracted from the culture broth by extraction and is subsequently chemically converted into free phytosphingosine, and into various ceramides.
An efficient acetylation is the basic requirement for the transport of the sphingoid bases into the culture medium: enzymatic tests with microsome fractions have shown that those strains with high productivity of acetylated sphingoid bases (high producers) display a markedly increased specific acetyltransferase activity compared to the low producers (Barenholz et al., 1971; Barenhoz et al., 1973). Hence this enzymatic activity could be identified as one of the main reasons for the efficient production of acetylated sphingoid bases by various Pichia ciferrii strains.
All attempts at purification, characterization and identification of such enzymes have hitherto failed, so that neither the proteins, nor the corresponding genes are known.
The purpose of the invention was to provide enzymes and coding sequences thereof which are capable of acetylating sphingoid bases.
DESCRIPTION OF INVENTION
Surprisingly it has been found that the enzymes described below are capable of solving the problem posed for the invention.
Isolated nucleic acids coding for acetyltransferases as described in the claims are therefore a subject of the present invention.
Recombinant cells which exhibit modified activity of the enzymes according to the invention are a further subject of the invention.
The acetyltransferases described with the present invention and the DNA sequences encoding them offer a number of advantages. They can be used for acetylating defined substrates (sphingoid bases) biotechnologically and highly specifically on various functional groups (hydroxy and amino groups). Compared to a chemical acetylation process, fewer side products are generated thereby, as a result of which the losses in yield and laborious purification steps can be minimized. The invention thus has great potential, especially for applications which require high product purity. Particularly high product purities are necessary inter alia in the cosmetics, food and luxury consumables and pharmaceuticals sectors, so that here the invention has particularly great potential. The biotechnological production of acetylated sphingoid bases can be effected with the present invention essentially in two different ways: firstly, the production can be effected via the biocatalysis approach, wherein selected sphingoid bases are enzymatically acetylated in a suitable reactor with addition of the acetyltransferase(s). Secondly, the genes of the acetyltransferases can be used to generate recombinant microbial strains by genetic engineering methods (Metabolic Engineering), which are capable of directly synthesizing acetylated sphingoid bases from simple C and N sources in a fermentative process. In comparison to a chemical process, the fermentative process is less expensive and ecologically more sustainable. Moreover, it is stereospecific, which is not ensured in a chemical total synthesis.
By use of only one of the acetyltransferases described in this invention, or the genes thereof, incompletely acetylated sphingoid bases can be specifically created. These can have particular biological effects and can thus be used for particular applications, e.g. as cosmetic or pharmaceutical active substances or precursors thereof.
Incompletely acetylated sphingoid bases can only be chemically prepared extremely laboriously, hence a considerable cost advantage arises for the biotechnological approach.
Unless otherwise stated, all percentages (%) stated are mass percent.
A contribution to the solution of the problem is provided by an isolated nucleic acid, which has a sequence selected from the groups [A1 to G1]
A1) a sequence according to Seq ID No. 1, wherein this sequence codes for a protein which is capable of converting phytosphingosine to triacetylphytosphingosine by transfer of the acetyl residues from three molecules of acetyl coenzyme A, B1) an intron-free sequence which is derived from a sequence according to A1) and which encodes the same protein or peptide as the sequence according to Seq ID No. 1 C1) a sequence which encodes a protein or peptide which includes the amino acid sequence according to Seq ID No. 2 and which is capable of converting phytosphingosine to triacetylphytosphingosine by transfer of the acetyl residues from three molecules of acetyl coenzyme A, D1) a sequence which is at least 70%, particularly preferably at least 90%, still more preferably at least 95% and most preferably at least 99% identical with a sequence according to one of the groups A1) to C1), particularly preferably according to group A1), wherein this sequence codes for a protein or peptide which is capable of converting phytosphingosine to triacetylphytosphingosine by transfer of the acetyl residues from three molecules of acetyl coenzyme A, E1) a sequence which hybridizes or would hybridize taking account of the degeneracy of the genetic code with the complementary strand of a sequence according to one of the groups A1) to D1), particularly preferably according to group A1), wherein this sequence codes for a protein or peptide which is capable of converting phytosphingosine to triacetylphytosphingosine by transfer of the acetyl residues from three molecules of acetyl coenzyme A, F1) a derivative of a sequence according to one of the groups A1) to E1), particularly preferably according to group A1) obtained by substitution, addition, inversion and/or deletion of at least one base, preferably of at least 2 bases, still more preferably of at least 5 bases and most preferably at least 10 bases but preferably of not more than 100 bases, particularly preferably of not more than 50 bases and most preferably of not more than 25 bases, wherein this derivative codes for a protein or peptide which is capable of converting phytosphingosine to triacetylphytosphingosine by transfer of the acetyl residues from three molecules of acetyl coenzyme A, G1) a complementary sequence to a sequence according to one of the groups A1) to F1), particularly preferably according to group A1).

A further contribution to the solution of the problem is provided by an isolated nucleic acid which has a sequence selected from the groups [A2 to G2]
A2) a sequence according to Seq ID No. 3, wherein this sequence codes for a protein which is capable of converting triacetylphytosphingosine to tetraacetylphytosphingosine by transfer of the acetyl residue from one molecule of acetyl coenzyme A, B2) an intron-free sequence which is derived from a sequence according to A2) and which encodes the same protein or peptide as the sequence according to Seq ID No. 3, C2) a sequence which encodes a protein or peptide which includes the amino acid sequence according to Seq ID No. 4, and which is capable of converting triacetylphytosphingosine to tetraacetylphytosphingosine by transfer of the acetyl residue from one molecule of acetyl coenzyme A, D2) a sequence which is at least 70%, particularly preferably at least 90%, still more preferably at least 95% and most preferably at least 99% identical with a sequence according to one of the groups A2) to C2), particularly preferably according to group A2), wherein this sequence codes for a protein or peptide which is capable of converting triacetylphytosphingosine to tetraacetylphytosphingosine by transfer of the acetyl residue from one molecule of acetyl coenzyme A, E2) a sequence which hybridizes or would hybridize taking account of the degeneracy of the genetic code with the complementary strand of a sequence according to one of the groups A2) to D2), particularly preferably according to group A2), wherein this sequence codes for a protein or peptide which is capable of converting triacetylphytosphingosine to tetraacetylphytosphingosine by transfer of the acetyl residue from one molecule of acetyl coenzyme A, F2) a derivative of a sequence according to one of the groups A2) to E2), particularly preferably according to group A2), obtained by substitution, addition, inversion and/or deletion of at least one base, preferably of at least 2 bases, still more preferably of at least 5 bases and most preferably at least 10 bases but preferably of not more than 100 bases, particularly preferably of not more than 50 bases and most preferably of not more than 25 bases, wherein this derivative codes for a protein or peptide which is capable of converting triacetylphytosphingosine to tetraacetylphytosphingosine by transfer of the acetyl residue from one molecule of acetyl coenzyme A, G2) a complementary sequence to a sequence according to one of the groups A2) to F2), particularly preferably according to group A2),

The “nucleotide identity” or “amino acid identity” is determined here by means of known methods. Special computer programs with algorithms taking account of specific requirements are generally used.
Preferred methods for the determination of identity firstly generate the greatest match between the sequences to be compared. Computer programs for the determination of identity include, but are not limited to, the GCG program package, including GAP (Deveroy, J. et at., Nucleic Acid Research 12 (1984), page 387, Genetics Computer Group University of Wisconsin, Medicine (Wi), and BLASTP, BLASTN and FASTA (Altschul, S. et al., Journal of Molecular Biology 215 (1990), pages 403-410. The BLAST program can be obtained from the National Center For Biotechnology Information (NCBI) and from other sources (BLAST Handbuch, Altschul S. et al., NCBI NLM NIH Bethesda ND 22894; Altschul S. et al., above).
The well-known Smith-Waterman algorithm can also be used for the determination of nucleotide identity.
Preferred parameters for the determination of “nucleotide identity” with use of the BLASTN program (Altschul, S. et al., Journal of Molecular Biology 215 (1990), pages 403-410, are:











Expect Threshold:
10


Word size:
28


Match Score:
1


Mismatch Score:
−2


Gap costs:
Linear



















The above parameters are the default parameters in the nucleotide sequence comparison.
The GAP program is also suitable for use with the above parameters.
Preferred parameters for the determination of “amino acid identity” with use of the BLASTP program (Altschul, S. et al., Journal of Molecular Biology 215 (1990), pages 403-410, are:











Expect Threshold:
10


Word size:
3


Matrix:
BLOSUM62


Gap costs:
Existence: 11; Extension: 1


Compositional
Conditional compositional score matrix


adjustments:
adjustment




















The above parameters are the default parameters in the amino acid sequence comparison.
The GAP program is also suitable for use with the above parameters.
In connection with the present invention, an identity of 60% according to the above algorithm means 60% identity. The same applies for higher identities.
The characteristic “sequence which hybridizes or would hybridize taking account of the degeneracy of the genetic code with the complementary strand of a sequence” designates a sequence which under preferably stringent conditions hybridizes or would hybridize taking account of the degeneracy of the genetic code with the complementary strand of a reference sequence. For example, the hybridizations can be performed at 68° C. in 2×SSC or according to the protocol of the digoxigenin-labeling kit from Boehringer (Mannheim). Preferred hybridization conditions are for example incubation at 65° C. overnight in 7% SDS, 1% BSA, 1 mM EDTA and 250 mM sodium phosphate buffer (pH 7.2) followed by washing at 65° C. with 2×SSC; 0.1% SDS.
The derivatives of the DNA isolated according to the invention which according to alternatives F1) or F2) can be obtained by substitution, addition, inversion and/or deletion of one or more bases of a sequence according to one of the groups A1) to E1) and A2) to E2) in particular include those sequences which in the protein which they encode lead to conservative amino acid replacements such as for example the replacement of glycine by alanine or of aspartic acid by glutamic acid. Such function-neutral mutations are described as sense mutations and lead to no fundamental change in the activity of the polypeptide. Furthermore, it is known that changes at the N and/or C terminus of a polypeptide do not significantly affect its function or can even stabilize this, so that correspondingly DNA sequences, in which bases are attached at the 3′ end or at the 5′ end of the sequence with the nucleic acids according to the invention are also encompassed by the present invention. Those skilled in the art find information on this inter alia in Ben-Bassat et al. (Journal of Bacteriology 169:751-757 (1987)), in O'Regan et a/. (Gene 77:237-251 (1989)), in Sahin-Toth et al. (Protein Sciences 3:240-247 (1994)), in Hochuli et al. (Bio/Technology 6:1321-1325 (1988)) and in well-known genetics and molecular biology textbooks.
The nucleic acid according to the invention is preferably a vector, in particular an expression vector or a gene overexpression cassette. Possible vectors are all vectors known to those skilled in the art which are usually used for the introduction of DNA into a host cell. These vectors can replicate either autonomously since they possess replication origins, such as for example that of the 2μ plasmid or ARS (autonomously replicating sequences), or integrate into the chromosomes (non-replicating plasmids). Vectors are also understood to mean linear DNA fragments which possess no replication origins whatever, such as for example gene insertion or gene overexpression cassettes. Gene overexpression cassettes usually consist of a marker, the genes to be overexpressed and regulatory regions relevant for the expression of the genes, such as for example promoters and terminators. Optionally, gene overexpression cassettes can also include specific DNA sequences which via homologous recombination mechanisms enable targeted integration into the host genome. Depending on the structure of the gene overexpression cassettes, these can preferably be integrated into the host genome in single or multiple form. Preferred vectors are selected from the group comprising plasmids and cassettes, such as for example E. coli -yeast shuttle plasmids, and expression vectors, gene insertion or gene overexpression cassettes are particularly preferable.
A contribution to the solution of the initially stated problem is provided by the cells described below, which can advantageously be used for the production of acetylated sphingoid bases, in particular acetylated phyosphingosine. The cells according to the invention can for example be contacted in a biotransformation with exogenously prepared sphingoid base, which the cells then acetylate by means of their enzyme equipment, or else cells which themselves already produce the sphingoid bases to be acetylated are used as starting strains for the production of the cells according to the invention.
Hence a subject of the present invention is a cell, preferably an isolated cell, characterized in that it has been genetically modified such that compared to the wild type thereof it has modified activity of at least one of the enzymes E 1 and/or E 2 , wherein the enzyme E 1 is selected from
an enzyme E 1 with the polypeptide sequence Seq ID No. 2 or with a polypeptide sequence in which up to 25%, preferably up to 20%, particularly preferably up to 15%, in particular up to 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1% of the amino acid residues are modified compared to the reference sequence Seq ID No. 2 by deletion, insertion, substitution or a combination thereof and which still possesses at least 10%, preferably 50%, particularly preferably 80%, in particular more than 90% of the enzymatic activity of the enzyme with the reference sequence Seq ID No. 2, wherein enzymatic activity for an enzyme E 1 is understood to mean the ability to convert phytosphingosine to triacetylphytosphingosine by transfer of the acetyl residues from three molecules of acetyl coenzyme A,

and the enzyme E 2 is selected from
an enzyme E 2 with the polypeptide sequence Seq ID No. 4 or with a polypeptide sequence in which up to 25%, preferably up to 20%, particularly preferably up to 15%, in particular up to 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1% of the amino acid residues are modified compared to the reference sequence Seq ID No. 4 by deletion, insertion, substitution or a combination thereof and which still possesses at least 10%, preferably 50%, particularly preferably 80%, in particular more than 90% of the enzymatic activity of the enzyme with the reference sequence Seq ID No. 4, wherein enzymatic activity for an enzyme E 2 is understood to mean the ability to convert triacetylphytosphingosine to tetraacetylphytosphingosine by transfer of the acetyl residue from one molecule of acetyl coenzyme A.
Herein, “wild type” designates a cell the genome whereof is present in a state which has arisen naturally through evolution. The term is used both for the whole cell and also for individual genes. Hence the term “wild type” in particular does not include those cells or those genes whose gene sequences have been at least partly modified by man by recombinant methods.
Preferably the modified activity is an increased activity. The term “increased activity of an enzyme” should preferably be understood as increased intracellular activity.
It is obvious to those skilled in the art that with regard to the term “modified (increased or decreased) activity compared to the wild type thereof”, cells or cell populations which are in identical, or comparable, states for example as regards growth phase, culture age and culturing phase, are compared.
The explanations that now follow on the increasing of the enzyme activity in cells apply both for the increasing of the activity of the enzyme E 1 to E 2 and also for all enzymes mentioned below, whose activity can if necessary be increased.
Essentially, an increase in the enzymatic activity can be achieved by increasing the copy number of the gene sequence or the gene sequences which code for the enzyme, using a strong promoter or an improved ribosome binding site, weakening a negative regulation of gene expression, for example with transcription regulators, or strengthening a positive regulation of gene expression, for example with transcription regulators, modifying the codon utilization of the gene, increasing the half-life of the mRNA or the enzyme in various ways, modifying the regulation of the expression of the gene or using a gene or allele which codes for a corresponding enzyme with increased activity and optionally combining these measures. Cells genetically modified according to the invention are for example created by transformation, transduction, conjugation or a combination of these methods with a vector which contains the desired gene, an allele of this gene or parts thereof and optionally a promoter enabling the expression of the gene. Heterologous expression in particular is achieved by integration of the gene or the allele into the chromosome of the cell or into an extrachromosomally replicating vector.
An overview of the possibilities for increasing the enzyme activity in cells in the case of pyruvate carboxylase is given in DE-A-100 31 999, which is herewith introduced as a reference and the disclosure content whereof regarding the possibilities for increasing enzyme activity in cells forms a part of the disclosure of the present invention. The expression of the above-mentioned and all below-mentioned enzymes and genes is detectable in gel by means of 1- and 2-dimensional protein gel separation followed by optical identification of the protein concentration with appropriate evaluation software. When the increasing of an enzyme activity is exclusively based on increasing the expression of the corresponding gene, then the quantification of the increase in the enzyme activity can be simply determined by comparison of the 1- or 2-dimensional protein separations between wild type and genetically modified cell. A common method for preparation of the protein gels in the case of coryneform bacteria and for identification of the proteins is the procedure described by Hermann et a/. (Electrophoresis, 22: 1712.23 (2001)). The protein concentration can also be analyzed by Western blot hybridization with an antibody specific for the protein to be detected (Sambrook et al., Molecular Cloning: a laboratory manual, 2nd Ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. USA, 1989) followed by optical evaluation with appropriate software for concentration determination (Lohaus and Meyer (1989) Biospektrum, 5: 32-39; Lottspeich (1999) Angewandte Chemie 111: 2630-2647). The activity of DNA-binding proteins can be measured by DNA band shift assays (also described as gel retardation) (Wilson et al. (2001) Journal of Bacteriology, 183: 2151-2155). The effect of DNA-binding proteins on the expression of other genes can be detected by various well-described methods of the reporter gene assay (Sambrook et al., Molecular Cloning: a laboratory manual, 2nd Ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. USA, 1989). Intracellular enzymatic activities can be determined by various described methods (Donahue et al. (2000) Journal of Bacteriology 182 (19): 5624-5627; Ray et al. (2000) Journal of Bacteriology 182 (8):2277-2284; Freedberg et al. (1973) Journal of Bacteriology 115 (3): 816-823). If no specific methods for the determination of the activity of a certain enzyme are stated in the following explanations, the determination of the increase in the enzyme activity and also the determination of the reduction of an enzyme activity is preferably performed by the methods described in Hermann et al., Electophoresis, 22: 1712-23 (2001), Lohaus et al., Biospektrum 5 32-39 (1998), Lottspeich, Angewandte Chemie 111: 2630-2647 (1999) and Wilson et al., Journal of Bacteriology 183: 2151-2155 (2001).
If the increasing of the enzyme activity is effected by mutation of the endogenous gene, then such mutations can be created either undirectedly by classical methods, such as for example by UV irradiation or by mutagenic chemicals, or specifically by genetic engineering methods such as deletion(s), insertion(s) and/or nucleotide substitution(s). Through these mutations, modified cells are obtained. Particularly preferable mutants of enzymes are in particular also those enzymes which are no longer or at least less feedback-, product- or substrate-inhibitable compared to the wild type enzyme.
If the increasing of the enzyme activity is effected by increasing the synthesis of an enzyme, then for example the copy number of the relevant gene is increased or the promoter and regulation region or the ribosome binding site which is located upstream of the structural gene is mutated. Expression cassettes which are incorporated upstream of the structural gene have a similar effect. Additionally, by means of inducible promoters it is possible to increase expression at any desired time. Further, however, so-called “enhancers” can also be assigned to the enzyme gene as regulatory sequences, which likewise cause increased gene expression via improved interaction between RNA polymerase and DNA. Expression is also improved by measures to prolong the lifetime of the mRNA. Moreover, enzyme activity is also intensified by prevention of the degradation of the enzyme protein. Here, the genes or gene constructs are present either in plasmids of different copy number or are integrated in the chromosome and if necessary amplified. Alternatively, moreover, overexpression of the relevant genes can be achieved by modification of the medium composition and culturing. Those skilled in the art find directions for this inter alia in Martin et al. (Bio/Technology 5, 137-146 (1987)), in Guerrero et al. (Gene 138, 35-41 (1994)), Tsuchiya and Morinaga (Bio/Technology 6, 428-430 (1988)), in Eikmanns et al. (Gene 102, 93-98 (1991)), in EP-A-0 472 869, in U.S. Pat. No. 4,601,893, in Schwarzer and Puhler (Bio/Technology 9, 84-87 (1991), in Reinscheid et al. (Applied and Environmental Microbiology 60, 126-132 (1994)), in LaBarre et al. (Journal of Bacteriology 175, 1001-1007 (1993)), in WO-A-96/15246, in Malumbres et al. (Gene 134, 15-24 (1993)), in JP-A-10-229891, in Jensen and Hammer (Biotechnology and Bioengineering 58, 191-195 (1998)) and in well-known genetics and molecular biology textbooks. The measures described above, like the mutations, also result in genetically modified cells.
To increase the expression of the particular genes, for example episomal or integrative plasmids are used. In principle, as plasmids or vectors, all embodiments available to those skilled in the art for this purpose are possible. Such plasmids and vectors can for example be inferred from the brochures of Novagen, Promega, New England Biolabs, Clontech or Gibco BRL. Further preferable plasmids and vectors can be found in: Glover, D. M. (1985) DNA cloning: a practical approach, Vol. I-III, IRL Press Ltd., Oxford; Rodriguez, R. L. and Denhardt, D. T (eds) (1988) Vectors: a survey of molecular cloning vectors and their uses, 179-204, Butterworth, Stoneham; Goeddel, D. V. (1990) Systems for heterologous gene expression, Methods Enzymol. 185, 3-7; and Sambrook, J.; Fritsch, E. F. and Maniatis, T. (1989), Molecular cloning: a laboratory manual, 2nd ed., Cold Spring Harbor Laboratory Press, New York.
The plasmid vector which contains the gene to be amplified is then transferred into the desired strain by conjugation or transformation. The method of conjugation is for example described in Schäfer et al., Applied and Environmental Microbiology 60: 756-759 (1994). Methods for transformation are for example described in Schorsch et al., Current Genetics 55(4): 381-389 (2009), Thierbach et al., Applied Microbiology and Biotechnology 29: 356-362 (1988), Dunican and Shivnan, Bio/Technology 7: 1067-1070 (1989) and Tauch et al., FEMS Microbiology Letters 123: 343-347 (1994). In the case of integrative plasmids or linear gene overexpression cassettes, these are integrated into the genome of the host strain either ectopically (not homologously) or specifically by homologous recombination mechanisms (“crossing over”). Depending on the exact structure of the plasmid or of the gene overexpression cassette and on the particular recombination event, the resulting strain contains one or several copies of the gene concerned.
The wording “an increased activity of an enzyme E x compared to the wild type thereof” used above and in the explanations below should preferably always be understood to mean an activity of the particular enzyme E x increased by a factor of at least 2, particularly preferably of at least 10, still more preferably of at least 100, still more preferably yet of at least 1,000 and most preferably of at least 10,000. Furthermore, the cell according to the invention which has “an increased activity of an enzyme E x compared to the wild type thereof”, in particular also includes a cell, the wild type whereof has no or at least no detectable activity of this enzyme E x , and which only displays detectable activity of this enzyme E x after increasing of the enzyme activity, for example by overexpression. In this connection, the term “overexpression” or the wording “increasing of expression” used in the explanations below also includes the case that a starting cell, for example a wild type cell, displays no or at least no detectable expression and detectable synthesis of the enzyme E x is only induced by recombinant procedures.
Changes of amino acid residues of a given polypeptide sequence which lead to no significant changes in the properties and function of the given polypeptide are well-known to those skilled in the art. Thus for example so-called conserved amino acids can be exchanged for one another; examples of such suitable amino acid substitutions are: Ala by Ser; Arg by Lys; Asn by Gln or His; Asp by Glu; Cys by Ser; Gln by Asn; Glu by Asp; Gly by Pro; His by Asn or Gln; Ile by Leu or Val; Leu by Met or Val; Lys by Arg or Gln or Glu; Met by Leu or Ile; Phe by Met or Leu or Tyr; Ser by Thr; Thr by Ser; Trp by Tyr; Tyr by Trp or Phe; and Val by Ile or Leu. Likewise, it is known that changes, particularly at the N or C terminus of a polypeptide for example in the form of amino acid insertions or deletions often exert no significant influence on the function of the polypeptide.
The activity of the enzyme E 1 is determined as described in Barenholz and Gatt, The Journal of Biological Chemistry 247 (21): 6827-6833 (1972), wherein phytosphingosine is used as substrate and the acetylation thereof compared to a reference system identical except for the property “containing as enzyme E 1 an enzyme with Seq ID No. 2” is measured.
The activity of the enzyme E 2 is determined as described in Barenholz and Gatt, The
Journal of Biological Chemistry 247 (21): 6827-6833 (1972), wherein triacetylated phytosphingosine is used as substrate and the acetylation thereof compared to a reference system identical except for the property “containing as enzyme E 2 an enzyme with Seq ID No. 4” is measured.
Cells preferred according to the invention exhibit intensified activity of both enzymes E 1 and E 2 .
In one preferable alternative of the invention, for the production of triacetyl phytosphingosine and the diacetylated sphingoid bases diacetyl sphingosine, diacetyl sphinganine, diacetyl-6-hydroxysphingosine and diacetyl sphingadienine, cells which have decreased activity of the enzyme E 2 compared to the wild type thereof are useful. In this connection, cells which as well as the decreased activity of the enzyme E 2 have increased activity of the enzyme E 1 are in particular useful.
Cells preferred according to the invention are microorganisms, in particular yeasts or bacteria, wherein preferable yeast cells in particular are selected from the genera Saccharomyces, Pichia, Yarrowia, Kluyveromyces, Hansenula, Ashbya and Candida, with the species Saccharomyces cerevisiae, Kluyveromyces lactis, Hansenula polymorpha, Pichia pastoris, Pichia ciferrii, Yarrowia lipolytica, Candida albicans, Candida utilis and Ashbya gossypii being particularly preferable.
It is particularly preferable according to the invention if for the production of the cells according to the invention starting strains are used which already have a high sphingoid bases titer; hence cells preferable according to the invention are in particular derived from the cells described in WO2006048458, WO2007131720 and DE102011110959.9 and from strains selected from the group consisting of Pichia ciferrii NRRL Y-1031 F-60-10 (Wickerham and Stodola, Journal of Bacteriology 80: 484-491 (1960), the Pichia ciferrii strains disclosed in the examples of WO 95/12683 and the strain Pichia ciferri CS.PCΔPro2, described in Schorsch et al., 2009, Curr Genet. 55, 381-9.
A further contribution to the solution of the problem posed for the invention is provided by the use of the cells according to the invention for the production of sphingoid bases and/or sphingolipids.
In connection with the present invention, the term “sphingoid bases” should be understood to mean phytosphingosine, sphingosine, sphingadienine, 6-hydroxy-sphingosine and sphinganine (dihydrosphingosine), also in the acetylated form, such as for example tetraacetylphytosphingosine, triacetylphytosphingosine, diacetylphytosphingosine, O-acetylphytosphingosine, triacetylsphinganine, diacetylsphinganine, O-acetylsphinganine, triacetylsphingosine, diacetylsphingosine, O-acetylsphingosine, tetraacetyl-6-hydroxysphingosine, triacetyl-6-hydroxysphingosine, diacetyl-6-hydroxysphingosine, O-acetyl-6-hydroxysphingosine, triacetyl-sphingadienine, diacetylsphingadienine and O-acetylsphingadienine. In connection with the present invention, the term “sphingolipids” should be understood to mean compounds which comprise sphingoid bases covalently linked with a fatty acid via an amide bond. The fatty acid can be saturated or singly or multiply unsaturated.
The length of the fatty acid side-chain can vary. The fatty acid side-chain can further possess functional groups such as hydroxy groups. The sphingolipids include for example phytoceramides, ceramides and dihydroceramides, and the more complex glucosylceramides (cerebrosides) and the inositol phosphorylceramides, mannosyl-inositol phosphorylceramides and mannosyl di-inositol phosphorylceramides. Also included here among the sphingolipids are sphingoid bases linked with an acetyl residue via an amide bond, such as for example N-acetylphytosphingosine, N-acetyl-sphinganine, N-acetylsphingosine, N-acetyl-6-hydroxysphingosine and N-acetyl-sphingadienine. These compounds are also known under the name short-chain ceramides.
In particular the use of the cells according to the invention for the production of sphingoid bases and/or sphingolipids selected from the group, phytosphingosine, sphingosine, 6-hydroxysphingosine, sphinganine (dihydrosphingosine), tetraacetyl-phytosphingosine (TAPS), triacetylphytosphingosine, diacetylphytosphingosine, O-acetylphytosphingosine, N-acetylphytosphingosine, triacetylsphinganine (TriASa), diacetylsphinganine, O-acetylsphinganine, N-acetylsphinganine, triacetylsphingosine (TriASo), diacetylsphingosine, O-acetylsphingosine, N-acetylsphingosine, tetraacetyl-6-hydroxysphingosine, triacetyl-6-hydroxysphingosine, diacetyl-6-hydroxysphingosine, O-acetyl-6-hydroxysphingosine, N-acetyl-6-hydroxysphingosine, triacetylsphingadienine, diacetylsphingadienine, O-acetylsphingadienine and N-acetylsphingadienine is advantageous. Quite especially preferable is the use of the cells according to the invention for the production of tetraacetylphytosphingosine (TAPS).
One preferable use according to the invention is characterized according to the invention in that cells preferable according to the invention as described above are used.
A further contribution to the solution of the problem posed for the invention is provided by a method for the production of sphingoid bases and/or sphingolipids comprising the process steps
a) contacting the cell according to the invention with a medium containing a carbon source, b) culturing the cell under conditions which enable the cell to form sphingoid bases and/or sphingolipids from the carbon source and c) optionally isolation of the sphingoid bases and/or sphingolipids formed.

Methods preferred according to the invention use cells mentioned above as preferred according to the invention.
As the carbon source, carbohydrates such as for example glucose, fructose, glycerin, saccharose, maltose and molasses, but also alcohols such as for example ethanol organic acids such as for example acetate are used. As the nitrogen source, for example ammonia, ammonium sulfate, ammonium nitrate, ammonium chloride, organic nitrogen compounds (such as yeast extract, malt extract, peptone, and corn steep liquor) can be used. Furthermore, inorganic compounds such as for example phosphate, magnesium, potassium, zinc and iron salts and others can be used. Suitable culturing conditions which enable the cell to form sphingoid bases and/or sphingolipids from the carbon source are known to those skilled in the art for Pichia ciferri for example from WO2006048458 and WO2007131720. Those skilled in the art can without the need for experiment apply these conditions to other cell types. The process according to the invention is particularly suitable for the production of tetraacetylphytosphingosine (TAPS), in particular when cells which exhibit intensified activity of both enzymes E 1 and E 2 are used.
The enzymes described can also advantageously be used for acetylation of the amino groups of aliphatic primary amines with 6 to 18 C atoms such as for example hexadecylamine.
Thus a further subject of the present invention is a method for the production of N-acetylated, primary aliphatic amines comprising the process steps
A) contacting at least one of the enzymes E 1 or E 2 , where the enzyme E 1 is selected from
an enzyme E 1 with the polypeptide sequence Seq ID No. 2 or with a polypeptide sequence in which up to 25%, preferably up to 20%, particularly preferably up to 15%, in particular up to 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1% of the amino acid residues are modified compared to the reference sequence Seq ID No. 2 by deletion, insertion, substitution or a combination thereof and which still possesses at least 10%, preferably 50%, particularly preferably 80%, in particular more than 90% of the enzymatic activity of the enzyme with the reference sequence Seq ID No. 2, wherein enzymatic activity for an enzyme E 1 is understood to mean the ability to convert phytosphingosine to triacetylphytosphingosine by transfer of the acetyl residues from three molecules of acetyl coenzyme A,
and the enzyme E 2 is selected from an enzyme E 2 with the polypeptide sequence Seq ID No. 4 or with a polypeptide sequence in which up to 25%, preferably up to 20%, particularly preferably up to 15%, in particular up to 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1% of the amino acid residues are modified compared to the reference sequence Seq ID No. 4 by deletion, insertion, substitution or a combination thereof and which still possesses at least 10%, preferably 50%, particularly preferably 80%, in particular more than 90% of the enzymatic activity of the enzyme with the reference sequence Seq ID No. 4, wherein enzymatic activity for an enzyme E 2 is understood to mean the ability to convert triacetylphytosphingosine to tetraacetylphytosphingosine by transfer of the acetyl residue from one molecule of acetyl coenzyme A,
with a medium containing a primary, aliphatic amine, in particular selected from those which have 6 to 18 carbon atoms, which are preferably linear, and Acetyl-CoA, and
B) optionally isolation of the acetylated amines formed.
Methods preferred according to the invention preferably use as enzymes E 1 and/or E 2 isolated and/or recombinantly produced enzymes and/or cells mentioned above as according to the invention.
In the examples presented below, the present invention is described by way of example, without it being intended that the invention, the range of application whereof emerges from the whole description and the claims, be restricted to the embodiments mentioned in the examples.


EXAMPLES
Overexpression of PcSLI1 in the Yeast Saccharomyces cerevisiae Strain K26
For the overexpression of PcSLI1 in Saccharomyces cerevisiae strain K26, the PcSLI1-ORF was firstly cloned into the 2μ vector p426HXT7-6HIS (Hamacher et al. Microbiology 148: 2783-2788 (2002), (Seq ID No. 6)). For this, the PcSLI1-ORF was amplified by polymerase chain reaction (PCR). Firstly, genomic DNA was isolated from P. ciferrii by a modified cethyltrimethylammonium bromide (CTAB) method (Murray and Thompson; Nucleic Acids Res 8, 4321-4325 (1980)). For this, cells of a culture grown in YEPD liquid medium (1% w/v yeast extract, 1% w/v peptone, 2% w/v glucose) (≧2 ml, OD 600nm >1) were harvested, resuspended in 400 μl CTAB buffer [2% (w/v) CTAB, 100 mM Tris-HCl (pH 8.0), 20 mM EDTA, 1.4 M NaCl], treated with 200 μl of glass beads (0.25-0.5 mm Ø) and disintegrated for 8 mins at 4° C. on a “Vibrax VXR basic” (2200 rpm). Next, the preparation was incubated for 30 mins at 65° C. After addition of one volume of chloroform followed by homogenization for 10 secs, the preparation was centrifuged for 5 mins at 16,000 g. The DNA-containing supernatant was removed and the DNA precipitated for at least 30 mins at −20° C. with 0.7 volumes of isopropanol. Then, after centrifugation for 15 mins at 16,000 g and 4° C., the sediment was washed with 70% ice-cold ethanol, dried and resuspended in 50 μl H 2 O.
The PCR amplification of the PcSLl1-ORF was then effected with genomic P. ciferrii DNA as template and with the two oligonucleotides SLI1.HXT7.fw (Seq ID No. 11) and SLI1.CYC1.ry (Seq ID No. 12). The primers used here each possessed at the 5′ end regions which were homologous with the integration region in the target vector. In S. cerevisiae, these homologous ends enable a homologous recombination between a linearized vector and PCR fragments in order to create a circularized plasmid which can be proliferated in vivo. As the DNA polymerase, the Phusion™ High-Fidelity DNA polymerase (Finnzymes) was used according to the manufacturer's directions. For the amplification, the following temperature profile was selected: step 1: 98° C., 2 mins (denaturation); step 2: 98° C., 15 secs (denaturation); step 3: 60° C., 25 secs (annealing);
step 4: 72° C., 80 secs (elongation); step 5: 72° C., 5 min (elongation). Steps 2-4 were repeated 35×. After agarose gel electrophoresis, the resulting 1.4 kb PCR fragment was purified using the “NucleoSpin® Extract II” gel extraction kit (Macherey-Nagel) according to the manufacturer's instructions.
The plasmid p426HXT7-6HIS (Seq ID No. 6) was digested with BamHI/EcoRI according to the manufacturer's instructions. After agarose gel electrophoresis, the resulting 6.3 kb vector fragment was also purified using the “NucleoSpin® Extract II” gel extraction kit (Macherey-Nagel) according to the manufacturer's instructions. The cloning of the PCR-amplified PcSLl1-ORF into the BamHI/EcoRI-cleaved vector was effected by in vivo recombination in S. cerevisiae. The basic method is described in Oldenburg et al. (Nucleic Acids Res 25: 451-452 (1994)). The two purified DNA fragments were transformed together into S. cerevisiae CEN.PK113-13D (K26), during which the protocol of Gietz and Schiestl (Nat Protoc 2: 31-34 (2007)) was followed. The cells were then plated out onto synthetic minimal medium (0.16% w/v yeast nitrogen base, 0.5% w/v ammonium sulfate, 2% w/v glucose, 2% w/v agar). Transformants could thereby be selected which on the basis of homologous recombination of the DNA fragment with the linearized vector possessed a stable, circularized plasmid. Plasmids were then isolated from the yeast clones. For this, cells of a 2 ml culture grown in synthetic minimal medium (OD 600nm >1) were harvested, washed and resuspended in 400 μl buffer 1 [50 mM glucose; 10 mM EDTA (Titriplex III); 25 mM Tris-HCl (pH 8); RNase A (100 μg/ml)]. After addition of 400 μl buffer 2 (0.2 M NaOH; 1% SDS) and careful mixing, ca. ⅔ of the volume of glass beads (0.25-0.5 mm ◯) were added and the cells disintegrated at 4° C. for 8 mins on a “Vibrax VXR basic” at 2200 rpm. 500 pl of supernatant were mixed with 250 μl buffer 3 [5 M potassium acetate (pH 5.5)], incubated for 10 mins on ice and centrifuged for 5 mins at 16,000 g. The supernatant was precipitated for at least 30 mins at −20° C. with isopropanol in the ratio 1:1 and then centrifuged for 20 mins at 16,000 g. The pelleted DNA was washed with 70% ethanol (−20° C.) and dissolved in 50 μl water. Next, the plasmid DNA was transformed into E. coli by electroporation as per Dower et al. (Nucleic Acids Res 16: 6127-6145 (1988)). For the electroporation, the Gene Pulser® was used under the following conditions: voltage: 2-2.5 kV; resistance: 200 Ω; capacitance: 25 μF. Transformants were selected on solid LB medium (1% w/v tryptone, 0.5% w/v yeast extract, 0.5% w/v NaCl, 2% Agar, pH 7.5) supplemented with 40 μg/ml ampicillin. For the isolation of the plasmids from E. coli, the clones were grown on a shaker overnight at 37° C. in 5 ml of liquid LB medium supplemented with 40 μg/ml ampicillin, then the GeneJET™ plasmid Miniprep Kit (Fermentas GmbH) was used according to the manufacturer's instructions.
The plasmids were then characterized by restriction analysis and sequencing. The correct integration of the PcSLI1-ORF into the linearized vector yielded the 7.6 kb plasmid pCS.426.SLI1 (Seq ID No. 7), in which the PcSLI1-ORF is under the control of the shortened HXT7 392-1 promoter fragment and the CYC1 terminator from S. cerevisiae. This arrangement enables a constitutive overexpression of PcSLI1 in S. cerevisiae.
The plasmids pCS.426.SLI1 (Seq ID No. 7) and the control plasmid p426HXT7-6HIS (Seq ID No. 6) were then transformed into S. cerevisiae strain K26, for which the method of Gietz and Schiestl (Nat Protoc 2: 31-34 (2007)) was again followed. Transformants were once again selected on synthetic minimal medium (0.16% w/v yeast nitrogen base, 0.5% w/v ammonium sulfate, 2% w/v glucose, 2% w/v agar). Next, the transformants were cultured in liquid TAPS medium [composition per liter: 33 g glucose monohydrate, 20 g potassium hydrogen phthalate, 4.83 g ammonium chloride, 1 g yeast extract, 1 g potassium dihydrogen phosphate, 0.88 g magnesium sulfate heptahydrate, 0.2 g calcium chloride dihydrate, 60 mg sodium chloride, 59 mg myoinositol, trace elements [37.3 mg ammonium-iron(II) sulfate hexahydrate, 7.5 mg copper(II) sulfate pentahydrate, 5 mg zinc sulfate heptahydrate, 1.5 mg potassium iodide, 0.6 mg manganese(II) sulfate monohydrate, 0.6 mg boric acid, 0.6 mg sodium molybdate dihydrate] and vitamins (3 mg nicotinic acid, 3 mg calcium D-pantothenate, 3 mg thiamine, 2 mg 4-aminobenzoic acid, 0.3 mg pyridoxine, 10 μg biotin); pH 5.4], in order to investigate the effect of the overexpression of PcSLI1 on the production of acetylated sphingoid bases. The transformants were grown aerobically at 30° C. on a rotary shaking device at 200-250 rpm. The cells were firstly grown in 5 ml TAPS as a preculture and on attainment of the stationary growth phase were used for the inoculation of 20 ml TAPS medium ( main culture).
Main cultures were started with an OD 600 nm of 0.1. For the analysis of acetylated sphingoid bases by LC-MS/MS, on attainment of the stationary phase 1 ml samples of the culture broth were withdrawn and stored at −20° C. until further processing. The extraction of the lipids was effected by the method of Bjerve et al. (Anal. Biochem. 58: 238-245 (1974)). For this, 20 μl of culture broth were taken up in ten times the volume of n-butanol. 20 ng of odd number C17 phytosphingosine, C17 sphinganine and deuterium-labeled d 9 triacetylsphinganine were added as internal standards and the sample was vigorously mixed at 70° C. Next, the sample was centrifuged at 1000× g for 5 mins, and 10 μl of the supernatant were withdrawn and diluted tenfold in 50/50% (v/v) methanol/H 2 O.
For the LC-MS/MS analysis of the sphingolipids, a Thermo Accela HPLC (Thermo Fisher Scientific Inc., Waltham, Mass., USA) unit was used. The injected sample volume was 5 μl. The column used was a reversed phase Hypersil Gold C18 column, thermostatted at 40° C. (1.9 μm particles; 50×2.1 mm; #25002-052130; Thermo Fisher Scientific Inc., Waltham, Mass., USA) and protected by a Microbore Guard column (Nucleodur C18 ISIS; 3 μm particles; 5×1 mm; #717759; Macherey-Nagel, Dueren, Germany). The mobile phase had a flow rate of 200 μl/min and consisted of (A) H 2 O with 0.1% v/v formic acid and 2% v/v acetonitrile, and (B) acetonitrile with 0.1% v/v formic acid. After 1 min initially with 70% B, a 4-step gradient was used for the elution: 1) increase from 70% B to 94% over 1.5 min; 2) increase from 94% B to 100% over 3.5 mins; 3) maintenance of 100% B over 3.5 mins; 4) reduction from 100% B to 70% and maintenance for 2.5 mins. The MS/MS analysis was performed as Multiple Reaction Monitoring (MRM) in the positive ionization mode. Applied mass transitions and collision energies are shown in table 1.





TABLE 1



Mass transitions and collision energies. IS, Internal standard

(deuterated or sphingolipid with odd number chain length).

Bold printed values were used as qualifiers.







Precursor
Product
Collision


ion
ion(s)
energy


(m/z)
(m/z)
(eV)



Sphinganine
302.3
284.4/ 266.4
10/ 25

C17-Sphinganine IS
288.3
270.4/ 252.4
10/ 25

Phytosphingosine
318.3
300.4/ 286.4
11/ 25

C17-Phytosphingosine IS
304.3
286.4/ 250.4
11/ 25

Triacetylsphinganine
428.3
368.4/ 266.4
10/ 25

Triacetylphytosphingosine
444.3
384.4/ 264.4
10/ 25

Tetraacetylphytosphingosine
486.3
426.4/ 264.4
10/ 25

d 9 -Triacetylsphinganine IS
437.3
374.4/ 266.4
10/ 25
































Instrument settings were as follows: capillary voltage, 3.5 kV; capillary temperature, 350° C., declustering voltage, 10 V; sheath gas pressure, 5 au (arbitrary units); ion sweep gas pressure, 0 au; auxiliary gas pressure, 5 au, S-lens RF amplitude, 50 V; collision energy, 10-35 eV; argon collision gas pressure, 1.0 mTorr; cycle length, 600 msecs; resolution of quadrupole 1 and 3 was 0.70 (fwhm). The Xcalibur software version 2.1 (Thermo Fisher Scientific Inc., Waltham, Mass., USA) was used for data recording and analysis.
The effect of PcSLI1 expression on the production of acetylated sphingoid bases in S. cerevisiae is shown in table 2. Markedly increased titers were mainly to be recorded in the case of diacetylsphinganine, triacetylsphinganine and triacetylphytosphingosine, while the quantity of tetraacetylphytosphingosine formed was unchanged in comparison to the control strain. This is a clear indication that the PcSLI1 protein can only transfer three acetyl residues onto phytosphingosine or sphinganine. This protein cannot however catalyze the final acetylation of triacetylphytosphingosine onwards to tetraacetylphytosphingosine.





TABLE 2



Production of acetylated and free sphingoid bases in recombinant S.

cerevisiae strains. K26L, strain S. cerevisiae K26 transformed with the control plasmid

p426HXT7-6HIS; K26SLI1, strain S. cerevisiae K26 transformed with the PcSLI1

overexpression plasmid pCS.426.SLI1; Sa, sphinganine; DiASa, diacetylsphinganine;

TriASa, triacetylsphinganine; Ps, phytosphingosine; TriAPS, triacetylphytosphingosine;

TAPS, tetraacetylphytosphingosine; the values show the titers in mg/l determined in the

fermentation broth.










Sa
DiASa
TriASa
Ps
TriAPS
TAPS











K26L
0.65
0
0.1
1.0
0
0.1

K26SLI1
0.4
1.5
0.7
0.6
1.4
0.1































Overexpression of PcSLI1 and PcATF1 in the Strain Saccharomyces cerevisiae Strain K26
For complete acetylation of phytosphingosine to tetraacetylphytosphingosine in Saccharomyces cerevisiae strain K26 the simultaneous overexpression of PcSLI1 and PcATF1 was required. For the overexpression of PcSLI1, the plasmid pCS.426.SLI1, the construction whereof was described in the previous example, is used. The expression vector p426HXT7-6HIS (Seq ID No. 6) used for this carries the S. cerevisiae URA3 marker gene. For the overexpression of PcATF1, the PcATF1-ORF must firstly be cloned into a suitable expression vector which carries an alternative marker gene. For this, the plasmid p425HXT7-6HIS (Becker and Boles; Appl Environ Microbiol 69: 4144-4150 (2003), (Seq ID No. 5)), which carries the S. cerevisiae LEU2 gene as selection marker, is used.
Firstly, the PcATF1-ORF including 19 by of the PcATF1 terminator is amplified from genomic P. ciferrii DNA by PCR. As primers, the oligonucleotides ATF2-HXT.fw (Seq ID No. 9) and ATF2-CYC.ry (Seq ID No. 10) are used. The primers used for this each possess at the 5′ end regions which are homologous to the integration region in the target vector. In S. cerevisiae, these homologous ends enable homologous recombination between a linearized vector and PCR fragments in order to create a circularized plasmid which can be proliferated in vivo.
As the DNA polymerase, the Phusion™ High-Fidelity DNA polymerase (Finnzymes) is used according to the manufacturer's instructions. For the amplification, the following temperature profile is selected: step 1: 98° C., 2 mins (denaturation); step 2: 98° C., 15 secs (denaturation); step 3: 61° C., 25 secs (annealing); step 4: 72° C., 80 secs (elongation); step 5: 72° C., 5 mins (elongation). Steps 2-4 are repeated 35×. After SDS gel electrophoresis, the resulting 1.6 kb PCR fragment is purified using the “NucleoSpin® Extract II” gel extraction kit (Macherey-Nagel) according to the manufacturer's instructions.
The plasmid p425HXT7-6HIS (Seq ID No. 5) is digested with BamHI/Hind111 according to the manufacturer's instructions. The resulting 7.5 kb vector fragment is also purified with the “NucleoSpin® Extract II” gel extraction kit (Macherey-Nagel) according to the manufacturer's instructions after SDS gel electrophoresis.
The cloning of the PCR-amplified PcATF1-ORF into the BamHI/EcoRl-cleaved vector is effected by in vivo recombination into S. cerevisiae. The basic method is described in Oldenburg et al. (Nucleic Acids Res 25: 451-452 (1994)). The two purified DNA fragments are transformed together into S. cerevisiae strain 10480-2C (MOsch and Fink, Genetics 145: 671-684 (1997)), for which the protocol of Gietz and Schiestl (Nat Protoc 2: 31-34 (2007)) is followed. The cells are then plated out onto minimal medium (0.16% w/v yeast nitrogen base, 0.5% w/v ammonium sulfate, 2% w/v glucose, 2% w/v agar) supplemented with 20 mg/I uracil. Thereby, transformants can be selected which because of homologous recombination of the DNA fragment with the linearized vector possess a stable, circularized plasmid. Plasmids are then isolated from the yeast clones. For this, cells from a 2 ml culture grown in synthetic minimal medium supplemented with 20 mg/I L-histidine HCl, 20 mg/I uracil and 20 mg/I L-tryptophan (OD 600nm >1) are harvested, washed and resuspended in 400 μl buffer 1 [50 mM glucose; 10 mM EDTA (Titriplex III); 25 mM Tris HCl (pH 8); RNase A (100 μg/ml)]. After addition of 400 μl buffer 2 (0.2 M NaOH; 1% SDS) and careful mixing, ca. % of the volume of glass beads (0.25-0.5 mm ◯) are added and the cells disintegrated at 4° C. for 8 mins on a “Vibrax VXR basic” at 2200 rpm. 500 μl of supernatant are mixed with 250 μl buffer 3 [5 M potassium acetate (pH 5.5)], incubated for 10 mins on ice and centrifuged for 5 mins at 16,000 g. The supernatant is precipitated for at least 30 mins at −20° C. with isopropanol in the ratio 1:1 and then centrifuged for 20 mins at 16,000 g. The pelleted DNA is washed with 70% ethanol (−20° C.) and dissolved in 50 μl water. Next, the plasmid DNA is transformed into E. coli by electroporation according to Dower et al. (Nucleic Acids Res 16: 6127-6145 (1988)). For the electroporation, the Gene Pulser® is used under the following conditions: voltage: 2-2.5 kV; resistance: 200 Ω; capacitance: 25 μF. Transformants are selected on solid LB medium (1% w/v tryptone, 0.5% w/v yeast extract, 0.5% w/v NaCl, 2% agar, pH 7.5) supplemented with 40 μg/ml ampicillin. For the isolation of the plasmids from E. coli, the clones are grown in 5 ml liquid LB medium supplemented with 40 μg/ml ampicillin overnight at 37° C. on a shaker, then the GeneJET™ plasmid miniprep kit (Fermentas GmbH) is used according to the manufacturer's instructions.
The plasmids are then characterized by restriction analysis and sequencing. The correct integration of the PcSLI1-ORF into the linearized vector yields the 8.9 kb plasmid pCS.425.ATF1 (Seq ID No. 8), in which the PcATF1-ORF is under control of the shortened HXT7 392-1 promoter fragment and the CYC1 terminators from S. cerevisiae. This arrangement enables constitutive overexpression of PcATF1 in S. cerevisiae.
For the simultaneous overexpression of PcSLI1 and PcATF2, the two plasmids pCS.426.SLI1 (Seq ID No. 7) and pCS.425.ATF1 (Seq ID No. 8) are then cotransformed into the S. cerevisiae strain 10480-2C, for which once again the method of Gietz and Schiestl (Nat Protoc 2: 31-34 (2007)) is followed. Transformants are selected on synthetic minimal medium (0.16% w/v yeast nitrogen base, 0.5% w/v ammonium sulfate, 2% w/v glucose, 2% w/v agar). For comparison purposes, the two starting plasmids p425HXT7-6HIS (Seq ID No. 5) and p426HXT7-6HIS (Seq ID No. 6) are also cotransformed into the strain RH2754. Next, the transformants are cultured in liquid TAPS medium in order to investigate the effect of the simultaneous over-expression of PcSLI1 and PcATF1 on the production of acetylated sphingoid bases. The transformants are grown aerobically at 30° C. on a rotating shaker at 200-250 rpm. The cells are firstly grown as a preculture in 5 ml TAPS and on reaching the stationary growth phase are used for the inoculation of 20 ml TAPS medium ( main culture). Culturing, processing of the samples and procedures for the determination of the production of acetylated sphingoid bases are effected analogously to the previous example.
In the case of the yeast strain transformed with the two plasmids pCS.426.SLI1 and pCS.425.ATF1, the analysis shows a markedly increased titer of tetraacetyl-phytosphingosine compared to the strain transformed with the two control plasmids (p425HXT7-6HIS and p426HXT7-6HIS). This is unambiguous evidence that the simultaneous overexpression of PcSLI1 and PcATF1 in Saccharomyces cerevisiae effects a complete acetylation of the metabolite phytosphingosine.