WO2007073847A1

WO2007073847A1 - Novel polypeptide having esterase activity and recombinant esterase and use thereof

Info

Publication number: WO2007073847A1
Application number: PCT/EP2006/011834
Authority: WO
Inventors: Gerhard Steinbauer; Michael Stanek; Peter Pojarliev; Wolfgang Skranc; Helmut Schwab; Marcel Wubbolts; Joannes Kierkels; Harald Pichler; Manuela Hermann; Christoph Zenzmaier
Original assignee: DSM Fine Chemicals Austria Nfg GmbH and Co KG
Current assignee: Patheon Austria GmbH and Co KG
Priority date: 2005-12-27
Filing date: 2006-12-08
Publication date: 2007-07-05
Anticipated expiration: 2008-06-27
Also published as: AT502991A1

Abstract

Polypeptide and recombinant protein having esterase activity which exhibit the amino acid sequence SEQ. ID. No. 1 and the use thereof.

Description

Novel polypeptide having esterase activity and recombinant esterase and use thereof

The invention relates to a novel polypeptide having esterase activity, and to an enzymatically active recombinant protein having esterase activity and to the use thereof in organic synthesis.

Esterases are generally employed in the resolution of racemates and asymmetrization.

However, only very few esterases suitable for preparing chiral compounds are commercially available. The use of esterase extracts from pig liver is known on the preparative scale. Pig liver esterase (PLE) was isolated long ago from natural sources, and its activity has also been known for a long time (Simonds, J. P. (1919) Amer. J. Physiol. 48, 141; Bamann, E. et al . (1934) Hoppe-Seyler Z. 229, 15; Falconer J. S. and Taylor, D. B. (1946) Biochem. J. 40, 831-834) . Various studies have also already been carried out in order to characterize PLE (Heymann, E. and Junge, W. (1979) Eur. J. Biochem. 95, 509-518; Lehner, R. and Verger, T. (1997) Biochemistry 36, 1861-1868) . However, the use of esterase extracts from natural sources, such as pig liver, is associated with disadvantages .

In the first place, the qualities of the different batches vary and thus make it difficult to optimize industrial processes. Secondly, the use of animal resources in the manufacture of pharmaceutical products is undesired because the presence of viruses and prions cannot always be precluded.

For these reasons there is a need to produce recombinant pig liver esterases of standardized quality in microorganisms.

The cloning of putative esterase genes is described for example in FEBS Lett. (1991), 293, 37-41. The first functional expression of an active pig liver esterase enzyme was described for the first time in WO 02/48322. WO 2004/055177 describes the preparation of further recombinant esterases by site directed mutagenesis of the recombinant pig liver esterase of seq. ID No. 1 (rPLE) from WO 02/48322. As is evident from the description of WO 2004/055177 and from the article authored by the same inventors in Protein Engineering, 16, 1139-1145, 2003, the modifications of the rPLE sequence from WO 02/48322 were chosen so that a recombinant intestinal pig esterase (PICE) disclosed in David et al . , (1998) Eur. J. Biochem. 257, 142-148, is obtained.

However, since the need for enzymatically active esterases which can easily be prepared biotechnologically is not met, it was an object of the present invention to provide a corresponding novel recombinant esterase.

In the attempt to isolate and to clone the gene described in FEBS Lett. (1991), 293, 37-41 and

WO 02/48322 for known pig liver esterase (PLE) as cDNA starting from mRNA from pig liver, a second, novel esterase sequence was found in addition to the known

PLE sequence. Following expression of the two sequences, in which the corresponding proteins or esterases, namely the known rPLE and a novel, recombinant "alternative" esterase (rAPLE) , was prepared, it unexpectedly emerged that the rAPLE has in some cases a different substrate spectrum than the known rPLE .

It was thus possible to achieve the object of the present invention by a novel polypeptide having esterase activity and a novel recombinant esterase (rAPLE) , whose amino acid sequence differs in 21 of a total of 548 amino acids from the known PLE sequence. The novel rAPLE differs in the amino acid sequence also from the known pig intestinal carboxylesterase (PICE) in 12 of a total of 548 amino acids. However, PICE is found in the pig intestinal tract.

The present invention accordingly relates to a polypeptide having esterase activity, which comprises the amino acid sequence SEQ. ID. No. 1.

The present invention further relates to a novel recombinant protein having esterase activity, which comprises the amino acid sequence SEQ. ID. No. 1.

The polypeptide and the recombinant rAPLE of the invention have the ability to resolve esters of the formula

(I) in which Rl and R2 are independently of one another a linear, branched or cyclic Ci-Ci₂-alkyl radical which may optionally also have one or more double or triple bonds or one or more atoms from the group of 0, S or N in the alkyl chain, and which may optionally be substituted by one or more substituents from the group of F, Cl, Br, NH₂, OH, d-C₆-alkyl, d-Cg-alkoxy, COOR3 , with R3 equal to C_x-C₆-alkyl , optionally mono- or poly- Ci~C₆-alkyl- or d-C₆-alkoxy-substituted C₆-C₂₀-aryl or -heteroaryl, optionally d-C₃-alkyl-substituted C₃-C₅- heterocycle having 1 or 2 atoms from the group of 0, S or N, or a C₆-C₂₀-aryl or -heteroaryl radical which may optionally be substituted by one or more substituents from the group of F, Cl, Br, NH₂, OH, Ci-C₆-alkyl or

Cχ-C₆-alkoxy, or in which Rl and R2 together form a C₂-Ci₂-alkylene radical which is optionally substituted by the abovementioned radicals.

The polypeptide and the recombinant rAPLE of the invention preferably have the ability to resolve racemic esters selectively. The polypeptide of the invention having esterase activity, and the novel recombinant esterase rAPLE differ, as stated above, in 21 of a total of 548 amino acids of the known sequence disclosed in FEBS Lett. (1991), 293, 37-41 and in 12 of a total of 548 amino acids from the known PICE protein disclosed in David et al., (1998) Eur. J. Biochem. 257, 142-148.

The sequence of the protein of the novel rAPLE of the invention differs in the following amino acid positions from the known sequence of the PLE protein:

APLE Position PLE

GIu 73 Asp

He 75 VaI

GIy 76 VaI

GIy 77 GIu

Leu 80 Thr

Arg 87 GIy

He 92 Thr

Pro 93 Leu

VaI 129 Leu

Ser 133 Pro

Thr 134 Met

Leu 138 VaI

Ala 139 VaI

Phe 234 Leu

Ala 236 VaI

GIy 237 Ala

Phe 286 Leu

Ala 287 Thr

Leu 290 Phe

Pro 294 GIn

Thr 302 Pro

The protein of the invention and the novel recombinant rAPLE may moreover be in the form of a modified sequence as shown in SEQ ID No 1, which can be obtained for example by usual modifications such as, for instance, insertion, exchange, deletion or attachment of amino acid(s) in the sequence at the N or C terminus, such as, for instance, GluAlaGluAla from the α factor signal sequence, or by fusion to other proteins.

The invention also further includes muteins having modifications within the protein sequence of the enzyme of the invention having the appropriate activity. Muteins can be obtained for example by modifications of the DNA which codes for the enzyme of the invention, by known mutagenesis techniques (random mutagenesis, site- directed mutagenesis, directed evolution, gene shuffling etc.) so that the DNA codes for an enzyme which differs at least by one amino acid from the enzyme of the invention, and subsequent expression of the modified DNA in a suitable host cell. The invention thus also includes modified DNA sequences as shown in SEQ ID. No 1, obtained by the mutations, deletions, insertions, extensions, fusions described above, and which code for enzymes having the desired esterase activity.

Estercise activity is defined in this connection as the ability to catalyze regioselective ester hydrolysis and chiral separation of racemic esters.

The polypeptide of the invention and the recombinant rAPLE can be prepared as described below:

Firstly, mRNA is isolated from pig liver using a suitable kit, and then the cDNA is generated by reverse transcription based on the mRNA extract. Subsequently, specific PCR primers based on the sequence of the known pig liver esterase gene of GenBank accesssion No. X63323 (Matsushima et al . , 1991) is prepared, followed by amplification and cloning. These specific primers are: Primer 1: 5'-CAGAATrCATGGCTATCGGGCAGCCAGCCTCGC-S' Primer 2: 5' -CCGGAATTCAGCCTCCCCTTCACAGCTCAG-3 '

This part of the primers which comprises the appropriate nucleotide sequences coding for the PLE protein and which is obligatorily present in the primers is in bold script.

The other sequence part of the primers comprises for example information for cleavage sites for restriction endonucleases (in italics) or sequence elements which are important for expression. This part may vary in the preparation of the rAPLE of the invention.

Amplification then takes place with primers 1 and 2 by prior art PCR methods.

The PCR product is subsequently used to prepare by prior art methods expression constructs for heterologous expression of the encoded rAPLE protein in suitable host organisms. This preferably entails the PCR product being initially cloned into suitable plasmid vectors.

The recombinant plasmids obtained in this way are then transformed into a suitable host, for example Escherichia coli. Inserts of several resulting clones are then sequenced.

Unexpectedly, 2 groups of recombinant clones with different sequences were identified therein, one being 100% identical to the expected sequence for PLE according to Matsushima et al . , (1991) FEBS Lett. 293, 37-41, and a novel nucleotide sequence as shown in SEQ. ED. No. 2 (APLE sequence) which leads after expression to the amino acid sequence SEQ. ID. No. 1 of the invention.

The present invention further relates to a nucleic acid or nucleotide sequence which codes for the polypeptide of the invention and the recombinant esterase rAPLE. For example, such a nucleic acid has the nucleotide sequence shown in SEQ. ID. No. 2.

The invention also relates further to nucleotide sequences which include a nucleotide sequence which codes for the polypeptide of the invention and the recombinant esterase rAPLE, or comprises the nucleotide sequence shown in SEQ. ID. No. 2.

A further possibility is to prepare appropriate oligonucleotides corresponding to nucleic acid sequences according to the present invention which code for the esterase of the invention by standardized synthetic techniques, for example with use of automated DNA synthesizers. The purely synthetic preparation of the nucleic acid sequences which code for the esterase of the invention is particularly advantageous for use in the production of pharmaceuticals or their intermediates, because enzymes are thus not obtained from animal sources.

Expression of the two sequences found (PLE and APLE sequences) then takes place.

The known pig liver esterase (PLE, Swiss-Prot ID Q29550) comprises an N-terminal signal sequence and a C-terminal ER retention signal, the last 4 amino acids HAEL.

In order to express the known PLE and the novel APLE, vectors in which the sequences are introduced into suitable expression systems constructed. These expression constructs are then transformed into suitable host cells.

Suitable host cells in this connection are for example microorganisms, animal cell lines and plants. Both prokaryotic and eukaryotic microorganisms can be employed. Preferred prokarytic hosts (bacteria) are

Escherichia coli, and strains from the genera Bacillus

(e.g. B. subtilis, B. licheniformis,

B.amyloliquefaciens), Pseudomonas (e.g. P. fluoresceins,

P.putida) , or Streptowyces (e.g. S.lividans, S.tendae) Eukaryotic microorganisms are preferred, and fungi are particularly preferred. Examples thereof are Saccharomyces cerevisiae, Pichia pastoris, Kluyveromyces lactis or Aspergillus sp.. Expression may be secretory or intracellular and both inducible and constitutive.

For bacterial expression a choice of species-specific signals can be obtained, a.o. as commercially available strains and vectors for protein expression (e.g provided by companies like Invitrogen, Novagen, New England Biolabs) , that allow inducible or constitutive expression, intracellular and secretory localization of the target protein; in addition, technology to enable or promote the correct folding of proteins in order to result in soluble and active protein may be applied.

The proteins are preferably expressed in a secretory manner:, in which case vectors in which the sequences of PLE and APLE are linked N-terminally to the α factor signal sequence of S. cerevisiae are preferably constructed.

It is further possible to prepare constructs in which the C-terminal tetrapeptide HAEL, which serves as ER retention signal as described for example in Hardwick et al., (1990) EMBO J. 9, 623-630, is additionally deleted.

A further preferred expression is inducible expression of constructs with or without ER retention signal . Unexpectedly, constructs having the ER retention signal can also be expressed and lead to an rAPLE which is capable of selective resolution of racemic esters.

The amino acid sequence of the novel esterase rAPLE which is derived from the nucleotide sequence of the APLE gene is depicted in SEQ ID No. 1.

It has unexpectedly been possible to find that the novel polypeptide or the rAPLE protein has, in contrast to the known rPLE, in each case obtained by expression of the DNA segments coding for APLE and PLE, respectively, for example in P. pastoris cells, in some cases a different substrate spectrum or increased activity.

The invention further relates to the use of the polypeptide having esterase activity or of the recombinant protein of the invention having the amino acid sequence shown in SEQ ID No. 1 or having at least 80% identity to the sequence shown in SEQ ID No. 1 in organic synthesis for ester cleavage. The polypeptide having esterase activity and the recombinant esterase

(rAPLE) of the invention preferably have at least 90%,

^■ particularly preferably at least 98%, identity to the sequence of the protein shown in SEQ ID No. 1. It is also possible to employ polypeptide having an esterase activity or the recombinant esterase (rAPLE) of the invention with modified DNA sequences shown in SEQ ID. No. 1, obtained by usual modifications such as, for instance, mutations, deletions, extensions, fusions, which code for enzymes having the desired esterase activity.

The polypeptide and the recombinant rAPLE of the invention are suitable for cleaving esters of the formula

(I) in which Rl and R2 are independently of one another a linear, branched or cyclic Ci-Ci₂-alkyl radical which may optionally also have one or more double or triple bonds or one or more atoms from the group of O, S or N in the alkyl chain, and which may optionally be substituted by one or more substituents from the group of F, Cl, Br, NH₂, OH, d-Cg-alkyl, d-Cg-alkoxy, COOR3 , with R3 equal to Ci-C₆-alkyl, optionally mono- or poly- Ci-Cs-alkyl- or Ci-C₆-alkoxy-substituted C₆-C₂₀-aryl or -heteroaryl, optionally Ci-C₃-alkyl-substituted C₃-C₅- heterocycle having 1 or 2 atoms from the group of 0, S or N, or a C₆-C₂₀-aryl or -heteroaryl radical which may optionally be substituted by one or more substituents from the group of F, Cl, Br, NH₂, OH, Ci-C₆-alkyl or Ci-C₆-alkoxy, or in which Rl and R2 together form a C₂-Ci₂-alkylene radical which is optionally substituted by the abovementioned radicals.

Ci-Ci₂-alkyl radicals mean in this connection linear, branched or cyclic alkyl radicals having 1 to 12 C atoms, such as, for instance, methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, tert-butyl, hexyl, cyclohexyl, etc.

It is also possible for one or more double to triple bonds to be present in the alkyl chain.

It is further possible for the alkyl chain to comprise one or more atoms from the group of 0, S or N. The alkyl radical may also be substituted one or more times. Suitable substituents in this connection are F, Cl, Br, NH₂, OH, d-Ce-alkyl, Ci-C₆-alkoxy or COOR3 , with R3 equal to Ci-C₆-alkyl.

Also suitable are optionally mono- or poly-Ci-Cg-alkyl- or C_L-C₆-alkoxy-substituted C_e-C₂₀-aryl or -heteroaryl radicals or an optionally Ci-C₃-alkyl-substituted C₃-C₅- heterocycle having 1 or 2 atoms from the group of 0, S or N.

Optionally substituted phenyl or naphthyl are preferred in this connection.

The radicals Rl and R2 may, however, also together form a C₂-Ci₂-alkylene radical, preferably C₄-Ci₂-alkylene radical, which is optionally substituted by the abovementioned radicals.

Examples of suitable substrates are α-methylphenyl- glycine esters, menthyl acetate, methyl succinate,

3-methyl glutarate, methyl 3- (4-methoxyphenyl) oxirane- 2-carboxylate, methyl mandelate, ibuprofen esters, solcetal esters, phenylethanol esters such as, for instance, 1-phenylpropyl butyrate or 1-phenyloctyl acetate, naproxen esters, 2-alkyl-5-halopent- 4-enecarboxylic esters, etc.

The polypeptide and the recombinant rAPLE of the invention are preferably employed for the resolution of racemic esters of the formula I .

The enzyme of the invention can moreover be used in any form. For example as dispersion, as solution, immobilized, as crude enzyme, as enzyme which has been obtained from its source by a combination of known purification methods, as whole cells (where appropriate immobilized and/or permeabilized) which have the required enzymatic activity (naturally or through genetic modifications) or in a lysate of such cells.

The reaction temperature for the conversions of the invention is normally between 0 and 9O⁰C, preferably between 10 and 6O⁰C. The pH of the reaction solution is between 4 and 11, preferably between 6 and 9. The reaction parameters, such as temperature, pH, solvent, etc., are chosen depending on the substrate chosen.

Example 1: mRNA isolation and generation of cDNA

0.7 g of liver from a freshly slaughtered pig, obtained from a local abattoir, was frozen in liquid nitrogen and homogenized with a mortar, and the liberated mRNA was isolated or extracted using the Fast Track mRNA extraction kit 2.0 (Invitrogen, Carlsbad, Calif., USA) in accordance with the statements made by the manufacturer (Fast Track 2.0 kit manual; version J; 082301; 25-0099) . The extraction afforded a total amount of 12.9 μg of mRNA.

0.26 μg of this mRNA was then used as template for generating cDNA using the Superscript III First-Strand synthesis system for RT-PCR according to the manufacturer's statements.

Example 2 : Amplification and cloning of cDNA fragments from pig liver

Specific primers based on the sequence of the pig liver esterase gene of GenBank accession No. X63323

(Matsushima et al . , 1991) were prepared:

Primer 1: δ'-CAGΛΛTTCATGGCTATCGGGCAGCCAGCCTCGC-S¹ (SEQ ID. No.3)

Primer 2: 5'-CCGGAA7TCAGCCTCCCCTTCACAGCTCAG -3¹ (SEQ ID No.4)

Bases homologous to the known PLE sequence are in bold script. Recognition sequences for restriction endonucleases are italicized for emphasis. The amplification took place in a 50 μl mixture with 1 U of Phusion DNA polymerase (Finnzymes, Espoo, Finland) , with 500 ng of cDNA as template, 20 μmol each of primer 1 and 2, 5 μl of a dNTP mix (2 mM each), all in lxPhusion HF buffer in accordance with * Phusion High-Fidelity DNA Polymerase' manual (Finnzymes) , starting with a 30 second denaturation step at 98°C, followed by 30 cycles (10 sec 98⁰C, 20 sec 68⁰C, 1 min 72°C) for amplification and a final incubation at 7O⁰C for 8 min to prepare complete products.

This PCR resulted in a DNA fragment with a size of 1.8 kb (found by agarose gel electrophoresis) . This PCR product was then purified using the Qiaquick kit (Qiagen, Hilden, Germany) in accordance with the manual included.

About 0.1 μg of the purified PCR product was cut with the restriction endonuclease EcoRI and cloned into the plasmid vectors pHILZ and pHIL-D2 via the EcoRI cleavage sites.

The vectors were then transformed into TOPlO electrocompetent cells prepared in accordance with 'Current Protocols in Molecular Biology'.

Inserts of several resulting clones were sequenced using the ^xDye Deoxy Terminator Cycle Sequencing' kit (Applied Biosystems Inc., Forster City, Calif., USA) . Two sequences were identified thereby, one corresponding 100% to the expected sequence published by Matsushima et al . , (1991) FEBS Lett. 293, 37-41, and the other sequence corresponding to SEQ ID No. 2.

Example 3 : Introduction of the α factor signal sequence and variations of the C-terminal end.

In order to enable secretory expression of the known protein PLE and the protein rAPLE of the invention, vectors in which the sequence of PLE and APLE was connected N-terminally to the α factor start sequence of the cloning vector pPICZ α (Invitrogen) were constructed. In addition, constructs in which the C-terminal tetrapeptide HAEL was deleted were prepared.

PCR I : The EcoRIalphal/alphaPLE2 primer pair was used to amplify the α factor signal sequence of the cloning vector pPICZ α (Invitrogen) . The PCR was carried out in a 50 μl mixture (2 ng of template, 0.5 μM of each primer, 0.2 mM dNTPs, 1 U of the Phusion DNA polymerase (Finnzymes) all in lxPhusion HF buffer in accordance with the 'Phusion High-Fidelity DNA Polymerase' manual

(Finnzymes) ) . Denaturation at 95⁰C for 3 minutes was followed by- amplification in 30 cycles (30 sec 95⁰C, 30 sec 57°C, 15 sec 72⁰C) and a final step at 72⁰C for 7 min.

PCR II: The PLE and APLE sequences were amplified from pHILZ plasmids using either the PLEalphal/EcoRIPLE+ER2 primer pair or the PLEalphal/EcoRIPLE2 (deletion of the C-terminal HAEL tetrapeptide) primer pair. These PCRs were again carried out in 50 μl mixtures (2 ng of template, 0.5 μM of each primer, 0.2 mM dNTPs, 1 U of the Phusion DNA polymerase (Finnzymes) all in lxPhusion HF buffer in accordance with the * Phusion High-Fidelity DNA Polymerase' Manual (Finnzymes) ) . A denaturation at 95⁰C for 3 minutes was followed by amplification in 30 cycles (30 sec 95⁰C, 30 sec 57⁰C, 15 sec 72°C) and a final step at 72⁰C for 7 min.

PCR III: 3 μl of the products from PCR 1 and PCR II were used to combine these two products by primerless PCR.

The extension was carried out in a 45 μl mixture with 0.2 mM dNTPs, I U of the Phusion DNA polymerase (Finnzymes) all in lxPhusion HF buffer.

The reaction mixture was heated at 95⁰C for 3 minutes and then 10 cycles with 30 sec at 95⁰C and 45 sec at 72⁰C were carried out. To amplify these overlapping extension products, 5 μl of primer mix (3 μl of water, 1 μl of 5 μM EcoRIalphal primer and 1 μl of 5 μM EcoRIPLE+ER2 or EcoRIPLE2 primer) were added. The products were amplified with 20 PCR cycles (30 sec

95°C, 30 sec 57⁰C, 1 min 72°C) and a single temperature stop at 72⁰C for 7 min. Primer sequences : EcoRlalphai : δ'-TCTTCGAAG/A/ATTCACGATGAGATTTCCTTCAATTTTTACTGC-S'

(SEQ ID No. 5) alphaPLE2: 5'-GAGGCTGGCTGCCCAGCTTCAGCCTCTCTTTTCTCG-S' (SEQ ID No. 6)

PLEalphal : 5'-AGAGAGGCTGAAGCTGGGCAGCCAGCCTCGCCG-S' (SEQ ID No. 7)

EcoRIPLE+ER2: 5'-ATGGr/4CCGΛA7TCTCACAGCTCAGCATGCTTTATCTTG-3' (SEQ ID No. 8)

EcoRIPLE2: 5'-ATGGTACCGAA πCTCACmATCTTGGGTGGCTTCTTTG-3¹ (SEQ ID No. 9)

Regions with homology to the templates in bold, recognition sequences for restriction endonucleases in italics .

Example 4 : Construction of expression constructs for the heterologous expression of pig liver esterases in Pichia pastoris

The overlapping extension PCR products from example 3 were purified using the Qiaquick kit (Qiagen, Hilden, Germany) in accordance with the manual included. About 0.1 μg of the purified PCR products was cut using the EcoRI restriction endonuclease and cloned via the EcoRI cleavage site into the plasmid vector pGAPZ A (Invitrogen) .

Correct orientation of the insert in relation to the promoters was checked with the aid of control cleavages, for example with Ncol .

In each case, a clone with correctly oriented insert was selected, sequenced and preserved. The corresponding plasmids were named as follows: Plasmids which contained the known PLE sequence as disclosed in Matsushima et al . , (1991) FEBS Lett. 293, 37-41, were called pGAPZ A PLE-ER (the HAEL tetrapeptide was deleted) and pGAPZ A PLE+ER (HAEL tetrapeptide still present) . Plasmids derived from the novel APLE sequence were called pGAPZ A APLE-ER (the HAEL tetrapeptide was deleted) and pGAPZ A APLE-ER (HAEL tetrapeptide still present) .

Example 5: Constitutive expression of pig liver esterases in Pichia pastoris

The plasmids pGAPZ A PLE-ER, pGAPZ A PLE+ER, pGAPZ A APLE-ER and pGAPZ A APLE+ER were transformed into P. pastoris X-33. The transformation took place in accordance with the instructions of the protocol for the Pichia Expressions kit from Invitrogen. The transformants were selected on YPD plates (1% yeast extract, 2% peptone, 2% D-glucose, 2% agar) which contained 100 mg/1 zeocin. 52 zeocin-resistant clones were streaked onto YPD plates with 100 mg/1 zeocin and preserved in 15% glycerol.

Example 6 : Qualitative analysis of the esterase activity

P. pastoris transformants were cultured on YPD plates with 100 mg/1 zeocin at 30⁰C for 48 h. The cells were lifted onto Whatman 541 hardened ashless 70 mm0 filters and air-dried. The filters were incubated with a solution of 6 mg of α-naphthyl acetate (Sigma, dissolved in 500 μl of acetone), 2.5 mg of tetrazotized o-dianisidine (Fast Blue Salt BN, Sigma, dissolved in 125 μl of water) and 5 ml of 0.1 M potassium phosphate buffer, pH 7, in order to visualize the esterase activity by a color reaction.

Activities were detected in all transformants which had integrated one of the 4 plasmids pGAPZ A PLE-ER, pGAPZ A PLE+ER, pGAPZ A APLE-ER and pGAPZ A APLE+ER. This proves the expression of functional proteins having esterase activity. As a check, a clone with integrated empty vector was also tested in the same way. In this case, no significant esterase activity was visible in the comparable reaction period. Example 7 : Stereoselective esterase activity in relation to methyl 5-chloro-2- (1-methylethyl) -4- pentenoate

P. pastoris transformants as described in example 6 were cultured on YPD plates with 100 mg/1 zeocin at 3O⁰C for 48 h. The cells were lifted onto Whatman 541 hardened ashless 70 mm0 filters and air-dried. The filters were incubated either with substrate solution A (100 μl of racemic methyl 5-chloro-2- (1-methylethyl) -4- pentenoate, 200 μl of 0.1 M potassium phosphate buffer, pH 8; 150 μl of 10 mg/ml phenol red; 450 μl of DMSO; 650 μl of H₂O) or with substrate solution B (identical to solution A but employing methyl (2S, 4E) -5-chloro-2- (1-methylethyl) -4 -pentenoate instead of the racemate) . Owing to the specific esterase activity on the substrates, the liberation of acid on hydrolysis of the ester substrate results in a pH decrease which in turn leads to a change in the color of the phenol red indicator to yellow.

It emerged from this that transformants containing the plasmid pGAPZ A APLE-ER gave signals (yellow coloration around the colony) after incubation for 3 to 4 hours if they were tested on substrate solution A, whereas no significant conversion could be found with substrate solution B (figure 1) .

Transformants obtained with the plasmids pGAPZ A PLE-ER or pGAPZ A PLE+ER showed no reaction with substrate solutions A or B under the same conditions. This showed that the recombinant rAPLE has a substrate specificity different from recombinant rPLE and that hydrolysis of methyl 5-chloro-2- (1-methylethyl) -4- pentenoate using rAPLE takes place stereoselectively for the (R) enantiomer.

Example 8: Comparison of rAPLE with PLE

The following substrates were tested in analogy to example 7 : Methyl 2R,3S-3- (4-methoxyphenyl) oxirane-2-carboxylate : activity of rAPLE; rPLE scarcely active

Dimethyl R, S-methylsuccinate : rAPLE very strong activity; rPLE strong activity

Dimethyl R, S-3-methylglutarate : rAPLE very strong activity; rPLE scarcely active

Example 9 : SDS polyacrylamide gel electrophoresis

10 μl of a 2x SDS sample buffer (125 mM Tris-HCl, pH 6.8; 4% SDS, 20% glycerol, 5% β-mercaptoethanol , 0.05% bromophenol blue) were added to 10 μl of commercially available pig liver esterase or 10 μl of the 60-fold concentrated (Centricon Ultrafiltrations-Spin Columns, from Sartorius) supernatants of the P. pastoris cultures (72 h at 100 rpm and 28⁰C in 250 ml of YPD medium in 2 1 Erlenmeyer flasks with baffles) which contained either the plasmid pGAPZ A APLE-ER or an empty pGAPZ A plasmid (control strain) .

After the samples had been heated at 95⁰C for 5 minutes, the proteins were separated on a 12.5% polyacrylamide gel (4% stacking gel) and stained with Coomassie Brilliant Blue R250 for detection. The SDS- PAGE shows a protein band with the expected size for rAPLE (~60 kDa) in the yeast strain having the pGAPZ A APLE-ER plasmid, but not in the control strain (figure 2) .

The commercially available pig liver esterase which was also analyzed for comparison showed two protein bands in the same size range (arrow in figure 2) .

Example 10: Induced expression of pig liver esterases with the AOXl promoter

The plasmids pGAPZ A PLE-ER, pGAPZ A PLE+ER, pGAPZ A APLE-ER and pGAPZ A APLE+ER were cut with the restriction endonuclease Xhol, and the respective fragments coding for APLE and PLE proteins, with or without ER retention signal, were cloned via the Xhol cleavage site into the pPIC9 vector (Invitrogen) . Correct orientation of the fragments in relation to the AOXl promoter was checked by means of control cuts with the restriction endonuclease Ncol . The vectors having the AOXl promoter were named, in analogy to the plasmids named in example 4, pPIC9 PLE-ER, pPIC9 PLE+ER, pPIC9 APLE-ER and pPIC9 APLE+ER, linearized with Sail and transformed into P. pastoris KM71. Transformation and selection for His prototrophy took place in accordance with the instructions of the Pichia expression kit from Invitrogen. Selected transformants and the KM71 strain were cultured on complete medium in accordance with the Pichia expression kit from Invitrogen overnight and induced with 1% methanol for 48 h. The resulting cultures were analyzed by means of the qualitative pH-shift assay described in example 7, testing 2 μl of the cultures in the mixtures in each case. Expression under the control of the inducible AOXl promoter led to very much higher, by comparison with the situation described for constitutive expression in example 7, rAPLE enzymic activities in relation to racemic methyl 5-chloro-2- (1-methylethyl) -

4-pentenoate . The phenyl red color change (red to yellow) was detectable after only a few minutes

(figure 3) . Unexpectedly, the rAPLE activity was independent of the presence of the ER retention signal HAEL at the C terminus, i.e. even cells which expressed rAPLE with ER retention signal showed activity. By contrast, yeast strains for producing rPLE had no activity in relation to racemic methyl 5-chloro-2- ( 1-methylethyl) -4-pentenoate.

Claims

1. A polypeptide having esterase activity and exhibiting the amino acid sequence SEQ. ID. No. 1.

2. A recombinant protein having esterase activity and exhibiting the amino acid sequence SEQ. ID. No. 1.

3. A polypeptide or recombinant protein which exhibits at least 80% identity to the amino acid sequence shown in SEQ ID No. 1 and has activity for resolution of esters of the formula

(I) in which Rl and R2 are independently of one another a linear, branched or cyclic Ci-Ci₂-alkyl radical which may optionally also have one or more double or triple bonds or one or more atoms from the group of 0, S or N in the alkyl chain, and which may optionally be substituted by one or more substituents from the group of F, Cl, Br, NH₂, OH, C¹i-Cs-alkyl, Ci-C₆-alkoxy, COOR3 , with R3 equal to Ci-C₆-alkyl, optionally mono- or poly-Ci-C₆-alkyl- or Ci-C₆-alkoxy-substituted C₆-C₂Q-aryl or -heteroaryl, optionally Ci-C₃-alkyl-substituted C₃-C₅-heterocycle having 1 or 2 atoms from the group of 0, S or N, or a C₆-C₂₀-aryl or -heteroaryl radical which may optionally be substituted by one or more substituents from the group of F, Cl, Br, NH₂, OH, Ci-C₆-alkyl or Ci-C₆-alkoxy, or in which Rl and R2 together form a C₂-Ci₂-alkylene radical which is optionally substituted by the abovementioned radicals.

4. A polypeptide or recombinant protein having esterase activity as claimed in any of claims 1-3, which exhibits an amino acid sequence modified by usual modifications from the group of mutation, deletion, insertion, extension and/or fusion.

5. A nucleotide sequence which codes for a polypeptide as claimed in claim 1 or a recombinant protein as claimed in claim 2.

6. A nucleotide sequence which has the sequence shown in SEQ ID No . 2.

7. A nucleotide sequence which comprises a nucleotide sequence as claimed in claim 5 or 6.

8. The use of a polypeptide or of a recombinant protein as claimed in claim 1, 2, 3 or 4 for resolution of esters of the formula

(0 in which Rl and R2 are independently of one another a linear, branched or cyclic Ci-Ci₂-alkyl radical which may optionally also have one or more double or triple bonds or one or more atoms from the group of O, S or N in the alkyl chain, and which may optionally be substituted by one or more substituents from the group of F, Cl, Br, NH₂, OH, C'i-C₆-alkyl, Ci-C₆-alkoxy, COOR3 , with R3 equal to Ci-C₆-alkyl, optionally mono- or poly-Ci-C_e-alkyl- or Ci-C₆-alkoxy-substituted C₆-C₂o-aryl or -heteroaryl, optionally Ci-C₃-alkyl-substituted C₃-C₅-heterocycle having 1 or 2 atoms from the group of 0, S or N, or a C₆-C₂₀-aryl or -heteroaryl radical which may optionally be substituted by one or more substituents from the group of F, Cl, Br, NH₂, OH, Ci-C₆-alkyl or Ci-C₆-alkoxy, or in which Rl and R2 together form a C₂-Ci₂-alkylene radical which is optionally substituted by the abovementioned radicals.