Highly selective anti-Prelog synthesis of optically active aryl alcohols by recombinant Escherichia coli expressing stereospecific alcohol dehydrogenase

Biocatalytic asymmetric synthesis has been widely used for preparation of optically active chiral alcohols as the important intermediates and precursors of active pharmaceutical ingredients. However, the available whole-cell system involving anti-Prelog specific alcohol dehydrogenase is yet limited. A recombinant Escherichia coli system expressing anti-Prelog stereospecific alcohol dehydrogenase from Candida parapsilosis was established as a whole-cell system for catalyzing asymmetric reduction of aryl ketones to anti-Prelog configured alcohols. Using 2-hydroxyacetophenone as the substrate, reaction factors including pH, cell status, and substrate concentration had obvious impacts on the outcome of whole-cell biocatalysis, and xylose was found to be an available auxiliary substrate for intracellular cofactor regeneration, by which (S)-1-phenyl-1,2-ethanediol was achieved with an optical purity of 97%e.e. and yield of 89% under the substrate concentration of 5 g/L. Additionally, the feasibility of the recombinant cells toward different aryl ketones was investigated, and most of the corresponding chiral alcohol products were obtained with an optical purity over 95%e.e. Therefore, the whole-cell system involving recombinant stereospecific alcohol dehydrogenase was constructed as an efficient biocatalyst for highly enantioselective anti-Prelog synthesis of optically active aryl alcohols and would be promising in the pharmaceutical industry.     

Gene cloning and expression of Leifsonia alcohol dehydrogenase (LSADH) involved in asymmetric hydrogen-transfer bioreduction to produce (R)-form chiral alcohols

The gene encoding Leifsonia alcohol dehydrogenase (LSADH), a useful biocatalyst for producing (R)-chiral alcohols, was cloned from the genomic DNA of Leifsonia sp. S749. The gene contained an opening reading frame consisting of 756 nucleotides corresponding to 251 amino acid residues. The subunit molecular weight was calculated to be 24,999, which was consistent with that determined by polyacrylamide gel electrophoresis. The enzyme was expressed in recombinant Escherichia coli cells and purified to homogeneity by three column chromatographies. The predicted amino acid sequence displayed 30-50% homology to known short chain alcohol dehydrogenase/reductases (SDRs); moreover, the NADH-binding site and the three catalytic residues in SDRs were conserved. The recombinant E. coli cells which overexpressed lsadh produced (R)-form chiral alcohols from ketones using 2-propanol as a hydrogen donor with the highest level of productivity ever reported and enantiomeric excess (e.e.).     

Quinoprotein alcohol dehydrogenase from ethanol-grown Pseudomonas aeruginosa.

Cell-free extracts of Pseudomonas aeruginosa strains, grown on ethanol, showed dye-linked alcohol dehydrogenase activities. The enzyme responsible for this activity was purified to homogeneity. It appeared to contain two molecules of pyrroloquinoline quinone per enzyme molecule. In many respects, it resembled other quinoprotein alcohol dehydrogenases (EC 1.1.99.8), having a substrate specificity intermediate between that of methanol dehydrogenases and ethanol dehydrogenases in this group. On the other hand, it also showed dissimilarities: the enzyme was found to be a monomer (Mr 101 000), to need only one molecule of the suicide substrate cyclopropanol to become fully inactivated, and to have a different aromatic amino acid composition.     

Quinohaemoprotein alcohol dehydrogenase apoenzyme from Pseudomonas testosteroni.

Cell-free extracts of Pseudomonas testosteroni, grown on alcohols, contain quinoprotein alcohol dehydrogenase apoenzyme, as was demonstrated by the detection of dye-linked alcohol dehydrogenase activity after the addition of PQQ (pyrroloquinoline quinone). The apoenzyme was purified to homogeneity, and the holoenzyme was characterized. Primary alcohols (except methanol), secondary alcohols and aldehydes were substrates, and a broad range of dyes functioned as artificial electron acceptor. Optimal activity was observed at pH 7.7, and the presence of Ca2+ in the assay appeared to be essential for activity. The apoenzyme was found to be a monomer (Mr 67,000 +/- 5000), with an absorption spectrum similar to that of oxidized cytochrome c. After reconstitution to the holoenzyme by the addition of PQQ, addition of substrate changed the absorption spectrum to that of reduced cytochrome c, indicating that the haem c group participated in the enzymic mechanism. The enzyme contained one haem c group, and full reconstitution was achieved with 1 mol of PQQ/mol. In view of the aberrant properties, it is proposed to distinguish the enzyme from the common quinoprotein alcohol dehydrogenases by using the name 'quinohaemoprotein alcohol dehydrogenase'. Incorporation of PQQ into the growth medium resulted in a significant shortening of lag time and increase in growth rate. Therefore PQQ appears to be a vitamin for this organism during growth on alcohols, reconstituting the apoenzyme to a functional holoenzyme.     

Enhancing cofactor recycling in the bioconversion of racemic alcohols to chiral amines with alcohol dehydrogenase and amine dehydrogenase by coupling cells and cell-free system

Alcohol dehydrogenase (ADH) and amine dehydrogenase (AmDH)-catalyzed one-pot cascade conversion of an alcohol to an amine provides a simple preparation of chiral amines. To enhance the cofactor recycling in this reaction, we report a new concept of coupling whole-cells with the cell-free system to enable separated intracellular and extracellular cofactor regeneration and recycling. This was demonstrated by the respective biotransformation of racemic 4-phenyl-2-butanol 1a and 1-phenyl-2-propanol 1b to (R)-4-phenylbutan-2-amine 3a and (R)-1-phenylpropan-2-amine 3b . Escherichia coli cells expressing S-enantioselective CpsADH, R-enantioselective PfODH, and NADH oxidase (NOX) was developed to oxidize racemic alcohols 1a–b to ketones 2a–b with full conversion via intracellular NAD⁺ recycling. AmDH and glucose dehydrogenase (GDH) were used to convert ketones 2a–b to amines (R)- 3a–b with 89–94% conversion and 891–943 times recycling of NADH. Combining the cells and enzymes for the cascade transformation of racemic alcohols 1a–b gave 70% and 48% conversion to the amines (R)- 3a and (R)-3 b in 99% ee, with a total turnover number (TTN) of 350 and 240 for NADH recycling, respectively. Improved results were obtained by using the E. coli cells with immobilized AmDH and GDH: (R)- 3a was produced in 99% ee with 71–84% conversion and a TTN of 1410-1260 for NADH recycling, the highest value so far for the ADH–AmDH-catalyzed cascade conversion of alcohols to amines. The concept might be generally applicable to this type of reactions.     

Zinc-activated alcohols in ternary complexes of liver alcohol dehydrogenase

Activation parameters for each reaction step in the kinetic mechanism of liver alcohol dehydrogenase have been measured for the oxidation of ethanol and the reduction of acetaldehyde. In the oxidation process, the highest enthalpy of activation, 9.7 kcal/mol, occurs for the turnover of the liver alcohol dehydrogenase-NAD(+)-ethanol ternary complex. To investigate if this enthalpy requirement represents a change in the ionization state of ethanol bound in the ternary complex, inhibition of ethanol oxidation was determined using the following series of small, electronegative alcohols with pKa values ranging from 12.37 to 15.5: 2,2,2-trifluoroethanol, 2,2,2-trichloroethanol, 2,2,2-tribromoethanol, 2,2-dichloroethanol, 2,2-difluoroethanol, propargyl alcohol, 3-hydroxypropionitrile, 2-chloroethanol, 2-iodoethanol, 2-methoxyethanol, ethylene glycol, and methanol. The observed inhibition patterns were analyzed according to several kinetic inhibition models; in each case, the best fit model was used to determine the substrate competitive inhibition constant. A plot of the logarithm of these inhibition constants is shown to be dependent on the pKa values of the inhibiting alcohols with a slope approaching -1, indicating that inhibition is controlled by a proton loss from the alcohol. The observed competitive inhibition behavior, coupled with crystallographic studies depicting a direct ligation of an alcohol oxygen to the catalytic zinc ion, indicates that inhibition is controlled by the formation of a zinc-bound alkoxide. Because the inhibiting alcohols are structurally homologous to ethanol, a relationship between the inhibition constant and the inhibiting alcohol's pKa can be derived to show that the pKa of an alcohol bound in a ternary complex is also dependent on its pKa as a free alcohol. Ternary complex pKa values have been determined for ethanol and the inhibiting alcohols.     

Characterization of four Rhodococcus alcohol dehydrogenase genes responsible for the oxidation of aromatic alcohols

Four genes were isolated and characterized for alcohol dehydrogenases (ADHs) catalyzing the oxidation of aromatic alcohols such as benzyl alcohol to their corresponding aldehydes, one from o-xylene-degrading Rhodococcus opacus TKN14 and the other three from n-alkane-degrading Rhodococcus erythropolis PR4. Various aromatic alcohols were bioconverted to their corresponding carboxylic acids using Escherichia coli cells expressing each of the four ADH genes together with an aromatic aldehyde dehydrogenase gene (phnN) from Sphingomonas sp. strain 14DN61. The ADH gene (designated adhA) from strain TKN14 had the ability to biotransform a wide variety of aromatic alcohols, i.e., 2-hydroxymethyl-6-methylnaphthalene, 2-hydroxymethylnaphthalene, xylene-α,α’-diol, 3-chlorobenzyl alcohol, and vanillyl alcohol, in addition to benzyl alcohol with or without a hydroxyl, methyl, or methoxy substitution. In contrast, the three ADH genes of strain PR4 (designated adhA, adhB, and adhC) exhibited lower ability to degrade these alcohols: these genes stimulated the conversion of the alcohol substrates by only threefold or less of the control value. One exception was the conversion of 3-methoxybenzyl alcohol, which was stimulated sevenfold by adhB. A phylogenetic analysis of the amino acid sequences of these four enzymes indicated that they differed from other Zn-dependent ADHs.The first two authors contributed equally to this work     

Rhodococcus erythropolis 手性醇脱氢酶的克隆表达及其性质

【目的】探讨红串红球菌中一种醇脱氢酶的性质及其对酮酯类及酮类底物的催化能力。【方法】从红串红球菌(Rhodococcus erythropolis ATCC 4277)中获取一段长度为1047 bp的醇脱氢酶(adh)基因,插入载体pET-22b(+)后,在大肠杆菌中进行重组表达。15℃的低温下用自诱导培养基诱导24 h,以苯乙酮为底物测定醇脱氢酶酶活。【结果】测得该诱导条件下重组菌体细胞破碎上清中醇脱氢酶酶活力为2.6 U/mg。经温度、pH耐受性等分析,发现该酶最适pH在6.0-6.5之间,耐受温度可以达到60℃,并且在该温度下保持5 h后,酶活也能保留80%。对于β酮酯类底物的催化反应,以对乙酰乙酸乙酯的催化能力最高。用4-氯乙酰乙酸乙酯(COBE)为底物进行全细胞水相催化反应,经手性液相色谱分析,发现在催化产物以R型4-氯-3羟基丁酸乙酯(CHBE)为主。【结论】该酶在酮酯类的底物转化方面有良好的开发潜力及应用前景。     

Enantioselective oxidation of secondary alcohols by quinohaemoprotein alcohol dehydrogenase from Comamonas testosteroni

Purified and reconstituted quinohaemoprotein alcohol dehydrogenase (QH-EDH) from Comamonas testosteroni is shown to oxidize secondary alcohols enantioselectively. The products formed during the oxidation of secondary alcohols were positively identified as the corresponding ketones. In the oxidation of chiral secondary n-alkyl alcohols a preference of the enzyme for the S(+)alcohols was found. The apparent kinetic parameters (K_m and K_max) for a range of n-alkyl alcohols depend on the length of the alcohol chain and the location of the hydroxyl function in the chain. The enzyme is stable up to a temperature of 37 °C. Above this temperature the activity is irreversibly lost. The pH optimum of the enzyme in the conversion of secondary alcohols is 7.7.     

Thermostable NAD-linked secondary alcohol dehydrogenase from propane-grown Pseudomonas fluorescens NRRL B-1244

NAD-linked alcohol dehydrogenase activity was detected in cell-free crude extracts from various propane-grown bacteria. Two NAD-linked alcohol dehydrogenases, one which preferred primary alcohols (alcohol dehydrogenase I) and another which preferred secondary alcohols (alcohol dehydrogenase II), were found in propane-grown Pseudomonas fluorescens NRRL B-1244 and were separated from each other by DEAE-cellulose column chromatography. The properties of alcohol dehydrogenase I resembled those of well-known primary alcohol dehydrogenases. Alcohol dehydrogenase II was purified 46-fold; it was homogeneous as judged by acrylamide gel electrophoresis. The molecular weight of this secondary alcohol dehydrogenase is 144,500; it consisted of four subunits per molecule of enzyme protein. It oxidized secondary alcohols, notably, 2-propanol, 2-butanol, and 2-pentanol. Primary alcohols and diols were also oxidized, but at a lower rate. Alcohols with more than six carbon atoms were not oxidized. The pH and temperature optima for secondary alcohol dehydrogenase activity were 8 to 9 and 60 to 70 degrees C, respectively. The activation energy calculated from an Arrhenius plot was 8.2 kcal (ca. 34 kJ). The Km values at 25 degrees C, pH 7.0, were 8.2 X 10(-6) M for NAD and 8.5 X 10(-5) M for 2-propanol. The secondary alcohol dehydrogenase activity was inhibited by strong thiol reagents and strong metal-chelating agents such as 4-hydroxymercuribenzoate, 5,5'-dithiobis(2-nitrobenzoic acid), 5-nitro-8-hydroxyquinoline, and 1,10-phenanthroline. The enzyme oxidized the stereoisomers of 2-butanol at an equal rate. Alcohol dehydrogenase II had good thermal stability and the ability to catalyze reactions at high temperature (85 degrees C). It appears to have properties distinct from those of previously described primary and secondary alcohol dehydrogenases.     

Crystal structure of quinone‐dependent alcohol dehydrogenase from Pseudogluconobacter saccharoketogenes. A versatile dehydrogenase oxidizing alcohols and carbohydrates

The quinone‐dependent alcohol dehydrogenase (PQQ‐ADH, E.C. 1.1.5.2) from the Gram‐negative bacterium Pseudogluconobacter saccharoketogenes IFO 14464 oxidizes primary alcohols (e.g. ethanol, butanol), secondary alcohols (monosaccharides), as well as aldehydes, polysaccharides, and cyclodextrins. The recombinant protein, expressed in Pichia pastoris, was crystallized, and three‐dimensional (3D) structures of the native form, with PQQ and a Ca²⁺ ion, and of the enzyme in complex with a Zn²⁺ ion and a bound substrate mimic were determined at 1.72 Å and 1.84 Å resolution, respectively. PQQ‐ADH displays an eight‐bladed β‐propeller fold, characteristic of Type I quinone‐dependent methanol dehydrogenases. However, three of the four ligands of the Ca²⁺ ion differ from those of related dehydrogenases and they come from different parts of the polypeptide chain. These differences result in a more open, easily accessible active site, which explains why PQQ‐ADH can oxidize a broad range of substrates. The bound substrate mimic suggests Asp333 as the catalytic base. Remarkably, no vicinal disulfide bridge is present near the PQQ, which in other PQQ‐dependent alcohol dehydrogenases has been proposed to be necessary for electron transfer. Instead an associated cytochrome c can approach the PQQ for direct electron transfer.     

Benzylic alcohols as stereospecific substrates and inhibitors for aryl sulfotransferase

Aryl sulfotransferase IV catalyzes the 3'-phosphoadenosine-5'-phosphosulfate (PAPS)-dependent formation of sulfuric acid esters of benzylic alcohols. Since the benzylic carbon bearing the hydroxyl group can be asymmetric, the possibility of stereochemical control of substrate specificity of the sulfotransferase was investigated with benzylic alcohols. Benzylic alcohols of known stereochemistry were examined as potential substrates and inhibitors for the homogeneous enzyme purified from rat liver. For 1-phenylethanol, both the (+)-(R)- and (-)-(S)-enantiomers were substrates for the enzyme, and the kcat/Km value for the (-)-(S)-enantiomer was twice that of the (+)-(R)-enantiomer. The enzyme displayed an absolute stereospecificity with ephedrine and pseudoephedrine, and with 2-methyl-1-phenyl-1-propanol; that is, only (-)-(1R,2S)-ephedrine, (-)-(1R,2R)-pseudoephedrine, and (-)-(S)-2-methyl-1-phenyl-1-propanol were substrates for the sulfotransferase. In the case of 1,2,3,4-tetrahydro-1-naphthol, only the (-)-(R)-enantiomer was a substrate for the enzyme. Both (+)-(R)-2-methyl-1-phenyl-1-propanol and (+)-(S)-1,2,3,4-tetrahydro-1-naphthol were competitive inhibitors of the aryl sulfotransferase-catalyzed sulfation of 1-naphthalenemethanol. Thus, the configuration of the benzylic carbon bearing the hydroxyl group determined whether these benzylic alcohols were substrates or inhibitors of the rat hepatic aryl sulfotransferase IV. Furthermore, benzylic alcohols such as (+)-(S)-1,2,3,4-tetrahydro-1-naphthol represent a new class of inhibitors for the aryl sulfotransferase.     

Functions of membrane-bound alcohol dehydrogenase and aldehyde dehydrogenase in the bio-oxidation of alcohols in Gluconobacter oxydans DSM 2003

In this study a new insight was provided to understand the functions of membrane-bound alcohol dehydrogenase (mADH) and aldehyde dehydrogenase (mALDH) in the bio-oxidation of primary alcohols, diols and poly alcohols using the resting cells of Gluconobacter oxydans DSM 2003 and its mutant strains as catalyst. The results demonstrated that though both mADH and mALDH participated in most of the oxidation of alcohols to their corresponding acid, the exact roles of these enzymes in each reaction might be different. For example, mADH played a key role in the oxidation of diols to its corresponding organic acid in G. oxydans, but it was dispensable when the primary alcohols were used as substrates. In contrast to mADH, mALDH appears to play a relatively minor role in organic acid-producing reactions because of the possible presence of other isoenzymes. Aldehydes were, however, found to be accumulated in the mALDH-deficient strain during the oxidation of alcohols.     

Purification and characterization of a novel alcohol dehydrogenase from Leifsonia sp. strain S749: a promising biocatalyst for an asymmetric hydrogen transfer bioreduction

To find microorganisms that could reduce phenyl trifluoromethyl ketone (PTK) to (S)-1-phenyltrifluoroethanol [(S)-PTE], styrene-assimilating bacteria (ca. 900 strains) isolated from soil samples were screened. We found that Leifsonia sp. strain S749 was the most suitable strain for the conversion of PTK to (S)-PTE in the presence of 2-propanol as a hydrogen donor. The enzyme corresponding to the reaction was purified homogeneity, characterized and designated Leifsonia alcohol dehydrogenase (LSADH). The purified enzyme had a molecular weight of 110,000 and was composed of four identical subunits (molecular weight, 26,000). LSADH required NADH as a cofactor, showed little activity with NADPH, and reduced a wide variety of aldehydes and ketones. LSADH catalyzed the enantioselective reduction of some ketones with high enantiomeric excesses (e.e.): PTK to (S)-PTE (>99% e.e.), acetophenone to (R)-1-phenylethanol (99% e.e.), and 2-heptanone to (R)-2-heptanol (>99% e.e.) in the presence of 2-propanol without an additional NADH regeneration system. Therefore, it would be a useful biocatalyst.     

Purification and characterisation of TOL plasmid-encoded benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase of Pseudomonas putida

Benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase, two enzymes of the xylene degradative pathway encoded by the plasmid TOL of a Gram-negative bacterium Pseudomonas putida, were purified and characterized. Benzyl alcohol dehydrogenase catalyses the oxidation of benzyl alcohol to benzaldehyde with the concomitant reduction of NAD+; the reaction is reversible. Benzaldehyde dehydrogenase catalyses the oxidation of benzaldehyde to benzoic acid with the concomitant reduction of NAD+; the reaction is irreversible. Benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase also catalyse the oxidation of many substituted benzyl alcohols and benzaldehydes, respectively, though they were not capable of oxidizing aliphatic alcohols and aldehydes. The apparent Km value of benzyl alcohol dehydrogenase for benzyl alcohol was 220 microM, while that of benzaldehyde dehydrogenase for benzaldehyde was 460 microM. Neither enzyme contained a prosthetic group such as FAD or FMN, and both enzymes were inactivated by SH-blocking agents such as N-ethylmaleimide. Both enzymes were dimers of identical subunits; the monomer of benzyl alcohol dehydrogenase has a mass of 42 kDa whereas that of the monomer of benzaldehyde dehydrogenase was 57 kDa. Both enzymes transfer hydride to the pro-R side of the prochiral C4 of the pyridine ring of NAD+.     

Conversion of green note aldehydes into alcohols by yeast alcohol dehydrogenase

Green note aldehydes were successfully reduced into their corresponding alcohol by commercial yeast alcohol dehydrogenase. Among different yeasts tested for their ability to convert (Z)-3-hexenal into (Z)-3-hexenol, Pichia anomala gave the best results. Conversion yields higher than 90% were also obtained by directly conducting the reaction in the medium where (Z)-3-hexenal is produced by the action of lipoxygenase and hydroperoxide lyase on linolenic acid.