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  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/24—Preparation of oxygen-containing organic compounds containing a carbonyl group
  • C12P7/26—Ketones
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C49/00—Ketones; Ketenes; Dimeric ketenes; Ketonic chelates
  • C07C49/20—Unsaturated compounds containing keto groups bound to acyclic carbon atoms
  • C07C49/24—Unsaturated compounds containing keto groups bound to acyclic carbon atoms containing hydroxy groups
  • C07C49/245—Unsaturated compounds containing keto groups bound to acyclic carbon atoms containing hydroxy groups containing six-membered aromatic rings
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
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  • C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
  • C12N9/88—Lyases (4.)

Definitions

• the invention relates to a process for the production of acyloin by enzymatic conversion of ⁇ -ketocarboxylic acids and / or aldehydes in the presence of pyruvate decarboxylase (PDC) and it includes a PDC suitable therefor and its production and the gene coding therefor.
• PDC pyruvate decarboxylase
• Acyloins or ⁇ -hydroxyketones are compounds with an optically active carbon atom that play a significant role in the synthesis of more complex compounds, such as, in particular, the (R) - (-) -phenylacetylcarbinol
• PAC which is of great economic interest for the production of ephedrine.
• R enantiomer is of interest, which is formed by fermentative conversion of pyruvate in the presence of benzaldehyde by means of Saccharomyces cerevisiae (DE-PS 548 459 from 1932).
• the pyruvate decarboxylase (PDC) isolated from the yeast also leads to considerable proportions of the 2-hydroxypropiophenone isomeric to PAC in this reaction.
• Such an enzymatic conversion also takes place starting from an aldehyde instead of ⁇ -ketocarboxylic acids, and the aldehyde formed by the decarbooxylation can also act as a "cosubstrate" in the condensation reaction with the formation of homoacyloins
• the PDC from Zymomonas mobilis has also been isolated.
• the process of the type mentioned at the outset is essentially characterized in that an enzyme is used as the PDC in which the tryptophan residue in the substrate channel leading to the active center is replaced by a sterically smaller amino acid residue.
• a sterically smaller amino acid residue is in particular a simple, in particular aliphatic, amino acid, such as specifically alanine, glycine,
• the genetically modified new PDC is obtained by replacing the codon TGG coding for tryptophan at position 392 in position 1174-1176 of the DNA sequence of the PDC gene from Z. mobilis in itself known manner and expression of the PDC in a producer organism, such as in particular E. coli, from which the PDC is isolated.
• the targeted mutation occurs e.g. B. using the polymerase chain reaction using the primers specified on page 9.
• the construction of the expression vector pBTac2 for the mutated PDC was carried out starting from the E. coli expression vector pPDC of the wild-type enzyme.
• the mutated PDC are obtained after harvesting and disruption of the cells from the crude extract in a manner known per se by chromatographic methods.
• An analogous optimization can generally be achieved with thiamine-diphosphate-dependent enzymes, which have an access limitation - be it steric or due to charge influences - in the substrate channel leading to the active center:
• an analogous modification of the DNA sequence of the coding for the enzyme Gene by replacing the codon coding for the access limitation with a codon coding for an amino acid residue which removes the access limitation, a significant increase in the synthesis capacity of the enzyme is achieved.
• linear and / or branched ⁇ -ketocarboxylic acids can be used as the substrate and aromatic, cyclic, longer-chain and / or branched aldehydes can be used as the substrate and / or cosubstrate.
• aromatic, cyclic, longer-chain and / or branched aldehydes can be used as the substrate and / or cosubstrate.
• aldehydes examples include benzaldehyde, cyclohexanaldehyde, furfural, cinnamaldehyde, crotonaldehyde, pyruvate, 2-ketobutyric acid, 2-ketopentanoic acid, 2-keto-4-methyllhexanoic acid,
• Fig. 1 The reaction scheme of the PDC for the example
• Fig. 2 A construction scheme for the formation of the expression vector containing the PDC from Z. mobilis pPDC and
• FIG. 3 A diagram for a production of PAC according to FIG. 1, which is optimized by trapping acetaldehyde by means of alcohol dehydrogenase.
• the vector pBTac2 (Boehringer, Mannheim) was chosen for the expression of the PDC from Zymomonas mobilis.
• the transcription of the foreign gene is under the control of the strong tac promoter, a hybrid of trp and lacUV promoters with 11-fold and 3-fold efficiency parent promoters.
• the operator sequence and ribosome binding region come from the lacZ gene.
• the transcription is thus regulated by the lac repressor of an overexpressing (laciQ) bacterial strain and can be induced by isopropyl- ⁇ -D-thiogalactoside (IPTG).
• the vector contains a single recognition sequence of the restriction endonuclease EcoRI, followed by the initiation codon ATG and then further restriction recognition sequences (sites), so that this vector is universal for expression both for gene sequences with and without its own
• Initiation codon can be used.
• the multiple cloning site is followed by the strong ribosomal RNA transcription terminators rrnB to ensure controlled termination of the transcription.
• the vector pZY134B (G. Sprenger, Inst. Biotechnologie 2, KFA-Jülich) was available as the starting material for cloning the PDC gene from Zymomonas mobilis (ATCC 29191). This plasmid contains a 3.2 kb DNA fragment from Zymomonas mobilis with the complete PDC gene including non-coding regions (FIG. 2). In order to enable the coding sequence to be ligated into the expression vector, it was necessary to introduce a new restriction recognition sequence in the 5 'direction of the initiation codon.
• PCR polymerase, chain reaction
• the required EcoRI restriction site was introduced in the 5 'direction of the initiation codon of the PDC gene by connecting the recognition sequence of the enzyme to the 5' end of the primer complementary to the gene during oligonucleotide synthesis. Since some endonucleases show a strongly reduced activity for the restriction of terminal sequences, four further bases were added upstream to the ECoRI site.
• the Taq polymerase most commonly used for PCR has no 3'-5 'exonuclease activity (proof-reading).
• the sequence it synthesizes is therefore subject to a statistical error rate. Even if this with the choice of suitable reaction conditions 1 / 100,000 can be kept very low, this necessitates the sequencing of each fragment to ensure the integrity of the synthesis. Therefore, not the entire coding region of the PDC gene (1712 bp), but a smaller fragment (890 bp) from the 5'-terminus to a single restriction site (EcoRV) was chosen for the amplification (FIG. 2).
• the PCR product was digested with the corresponding restriction endonucleases EcoRI and EcoRV.
• the missing second part of the PDC gene was obtained from the plasmid pZY134B by restriction with ECoRV and BamHI, the resulting fragment (1.2 kb) at the 3 'end still containing about 350 bp untranslated sequence of the PDC gene. Both fragments were separated by preparative agarose gel electrophoresis, isolated and ligated in the EcoRI and BamHI linearized, isolated pBTac2 (4.6 kb). The cloning was carried out in E. coli JM 109, a strain overexpressing the lac repressor.
• the PDC gene from Z. mobilis in the E. coli expression vector pPDC was available as a starting point (see FIG. 2). DNA isolation was carried out according to standard methods (J. Sambroch, E.F. Fritsch, T. Maniatis, Molecular Cloning (1989) Sping Harbor Laboratory Press). The plasmid pPDC served as a template for the synthesis of the two overlapping individual fragments.
• the primers J. Sambroch, E.F. Fritsch, T. Maniatis, Molecular Cloning (1989) Sping Harbor Laboratory Press.
• Tm 2 * (A + T) + 3 * (C + G)
• the fragments were separated electrophoretically, isolated, precipitated for concentration with ethanol and taken up again in Tris-HCl buffer, 10 mM, pH 7.4.
• the numbering refers to the 1st (5 ') nucleotide of the PDC sequence
• the mutated bases are underlined.
• this primer is complementary to the vector sequence at the 3 'end following the PDC sequence
• PDC-W392A An enzyme according to the invention (PDC-W392A) was obtained by expression of the modified DNA in E. coli cells.
• the mutated enzyme (mutant) PDC-W392A was expressed according to the following procedure and purified from the cell extract:
• the E. coli cells carrying the expression plasmid for the mutant PDC-W392A were fermented for selection in LB medium including 100 ⁇ g / ml ampicillin.
• the medium was inoculated with pre-cultures in the stationary growth phase in a ratio of 1:50 and at 37 ° C and
• the expression was carried out as described above in an 8 liter fermenter. A pH value of 7.0 and an air flow of 10 l / h were set. The stirring speed was 200 rpm. To avoid excess
• Foaming was added to polypropylene glycol as needed.
• the cells were harvested after 3 hours of expression by chilled continuous centrifugation.
• the digestion was carried out by grinding with glass beads.
• the digestion was carried out in Eppendorf vessels in a Retsch mill or ice-cooled in the Disintegrator S (maximum volume 80 ml). The grinding took place over 10 minutes with maximum performance.
• the suspension was centrifuged, the glass beads washed with buffer and the combined centrifugates filtered (1 ⁇ m).
• the PDC mutants were purified by column chromatography as follows: 1. Anion exchange chromatography
• the crude extract (approx. 110 ml, approx. 1.0-1.5 g protein) was applied to a Q-Sepharose Fast Flow (Pharmacia)
• the combined fractions were adjusted to an ammonium sulfate content of 50% saturation by adding a volume of saturated ammonium sulfate solution.
• the hydrophobic interaction chromatography was carried out on Butyl Sepharose (Pharmacia) (column 5 * 8 cm) at a flow rate of 2 ml / min.
• the material was equilibrated before loading with 40% ammonium sulfate in 50mM Mes / KOH, 2mM MgCl 2 , 0.1mM ThDP.
• the enzyme eluted in the same buffer with a falling ammonium sulfate gradient (40-0%) at 24%.
• the target fractions were again identified using an activity test and pooled (approx. 160 ml).
• the determination of the enzymatic activity was carried out in the coupled enzymatic test, the NADH oxidation being monitored photometrically by the auxiliary enzyme alcohol dehydrogenase from yeast (EC 1.1.1.1).
• the reaction mixture contained 16.9 mM pyruvate, 0.18 mM NADH and 10 U ADH in 50 mM Mes / KOH, pH 6.5, 20 mM MgSO 4 , 1.5 mM ThDP.
• One enzyme unit PDC (1 U) corresponds to the amount of enzyme that catalyzes the conversion of 1 ⁇ mol substrate in one minute at 30 ° C.
• the enzyme activity is calculated according to:
• Chiral acyloins can be obtained starting from an ⁇ -ketocarboxylic acid or an aldehyde as substrate and a further aldehyde as cosubstrate by means of PDC or PDC mutants.
• PAC synthesis starting from pyruvate and benzaldehyde The synthesis mixture contained 40 mM pyruvate, 70 mM benzaldehyde and 10 U / ml PDC-W392A in Mes / KOH buffer, 50 mM, pH 6.5, 20 mM MgSO 4 , 1.5 mM ThDP. The reaction was carried out for one hour at 37 ° C and the resulting PAC (6.2 mM) was detected by HPLC.
• PAC synthesis approach contained 40 mM acetaldehyde instead of pyruvate. Otherwise the procedure was as described above. After one hour, 3.7 mM PAC had developed.
• the enzymatic conversion was carried out according to FIG. 3.
• the use of alcohol dehydrogenase (ADH) from yeast (EC 1.1.1.1) enables the continuous removal of acetaldehyde and the inactivation of the PDC-W392A which is caused thereby.
• the formate dehydrogenase (FDH) from Candida boidinii (EC 1.2.1.2) is used to regenerate NADH.
• the enzymatic PAC synthesis was carried out in 20 ml of Mes / KOH buffer, 50 mM, pH 6.5, 20 mM MgSO 4 , 1.5 mM ThDP.
• reaction products were separated using preparative reversed-phase HPLC.
• Elution was carried out under isocratic conditions with acetic acid / acetonitrile 0.5% / 12.5% (v / v) at a flow rate of 1.5 ml / min. Under these conditions, the elution times were: PAC, 4.77 min and 2-hydroxypropiophenone, 5.41 min.
• the enantiomer as R - (-) - PAC was assigned using polarimetry using a standard from PAC production (Knoll AG).
• the enantiomer ratio of PAC was determined by chiral gas chromatography to be >> 98%.

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• 1995
  • 1995-06-29 DE DE19523269A patent/DE19523269C2/de not_active Expired - Fee Related
• 1996
  • 1996-05-22 JP JP8535270A patent/JPH11505710A/ja active Pending
  • 1996-05-22 CZ CZ19973691A patent/CZ287619B6/cs not_active IP Right Cessation
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