•Discover a novel alcohol dehydrogenase (named as KleADH) from Klebsiella oxytoca by a genome mining method.•First alcohol dehydrogenase from proteobacterial for synthesis of t-butyl 6-chloro-(3R,5S)-dihydroxyhexanoate with high enantioselectivity.•A systematic study of several factors influencing the whole-cell catalyst activity such as temperature, pH, the effects of metal ions and organic solvent was performed.•KleADH exhibited notable activity towards several aryl ketones with high stereoselectivity.Alcohol dehydrogenases can catalyze the inter-conversion of aldehydes and alcohols. The t-butyl 6-chloro-(3R,5S)-dihydroxyhexanoate is a key chiral intermediate in the synthesis of statin-type drugs such as Crestor (rosuvastatin calcium) and Lipitor (atorvastatin). Herein, a novel alcohol dehydrogenase (named as KleADH) discovered from Klebsiella oxytoca by a genome mining method was cloned and characterized. The KleADH was functionally overexpressed in Escherichia coli Rosetta (DE3) and the whole cell biocatalyst was able to convert t-butyl 6-chloro-(5S)-hydroxy-3-oxohexanoate to t-butyl 6-chloro-(3R,5S)-dihydroxyhexanoate with more than 99% diastereomeric excess (de) and 99% conversion in 24 h without adding any expensive cofactors. Several factors influencing the whole cell catalyst activity such as temperature, pH, the effects of metal ions and organic solvent were determined. The optimum enzyme activity was achieved at 30 °C and pH 7.0 and it was shown that 1 mM Fe3+ can increase the enzyme activity by 1.2 times. N-hexane/water and n-heptane/water biphasic systems can also increase the activity of KleADH. Substrate specificity studies showed that KleADH also exhibited notable activity towards several aryl ketones with high stereoselectivity. Our investigation on this novel alcohol dehydrogenase KleADH reveals a promising biocatalyst for producing chiral alcohols for preparation of valuable pharmaceuticals.Download high-res image (127KB)Download full-size image

•A novel (R)-selective amine transaminase (ATFo) was discovered from Fusarium oxysporum through genome mining method.•The purified ATFo demonstrated high stereoselectivity towards (R)-enantiomer of α-phenethylamine, which indicated its (R)-selectivity.•The discovery of the (R)-selective amine transaminase ATFo was a valuable contribution to the currently small toolbox of these enzymes.Amine transaminases are prominent biocatalysts in the production of chiral amines which are indispensable building blocks in asymmetric synthesis. In this study, a new (R)-enantioselective amine transaminase from Fusarium oxysporum (ATFo) was identified by genome mining. ATFo possibly evolved from a branched chain amino acid aminotransferase (BCAT) with key amino acids being changed, which belong to one of the three groups of pyridoxal 5′-phosphate dependent enzymes class IV (PLPDE_IV). The gene of the amine transaminase was functionally expressed and the protein was then purified with a molecular mass of approximately 36 kDa. The purified ATFo demonstrated high stereoselectivity towards (R)-enantiomer of α-phenethylamine and other analogues, which clearly indicated its (R)-selectivity. The optimal temperature and pH for the activities of ATFo were 25 °C and 7.0, respectively. Addition of Mn2+ and Zn2+ could greatly enhance the enzyme activity. In addition, the specific activities and stereoselectivities of these ATFo toward various amino donors and amino acceptors were determined. Compared to (S)-selective amine transaminase, the (R)-selective counterpart has been less studied. Given their pivotal role in asymmetric biocatalysis, it is of great importance to find more (R)-selective amine transaminases with ability or potential for synthesis of the target compounds. Thus, the discovery of the (R)-selective amine transaminase ATFo is a valuable contribution to the currently small toolbox of these enzymes.Download high-res image (95KB)Download full-size image

2-Azabicyclo[2.2.1]hept-5-en-3-one (γ-lactam) is an important precursor of many carbocyclic nucleoside analogs and pharmaceuticals. (−)-γ-Lactam has attracted much attention because of its role as an intermediate of antiviral drugs such as abacavir and carbovir. (+)-γ-Lactamase can be used for the kinetic resolution of γ-lactam to obtain (−)-γ-lactam. In this study, a novel (+)-γ-lactamase (Mh33H4-5540) was discovered from the gene library of Microbacterium hydrocarbonoxydans based on a colorimetric high-throughput screening method and it could be used to enantioselectively catalyze the bioresolution of racemic γ-lactam with high enantiomeric excess (ee) (>99 %) and yield (>49 %). An unexpected finding was that Mh33H4-5540 was unrelated to other known γ-lactamases (5.7, 4.8, 7.2, and 5.4 % similarities in amino sequence with (+)-γ-lactamase from Comamonas acidovorans, Bradyrhizobium japonicum, Aeropyrum pernix, and Sulfolobus solfataricus, respectively) but rather related to isochorismatases. The homolog analysis of Mh33H4-5540 revealed that it was similar in structure with bacterial isochorismatases (an isochorismatase from Pseudomonas putida (PDB number 4H17) and a putative isochorismatase from Oleispira antarctica (PDB number 3LQY)). Thus, Mh33H4-5540 represented another type of (+)-γ-lactamase. Mh33H4-5540 was overexpressed in E. coli Rosetta (DE3), purified to homogeneity and functionally characterized. The enzyme displayed optimal activity at 25 °C and pH 8.0. The activity showed a 5.5-fold increase in the presence of 0.5 M Ni2+ or Co2+. Mh33H4-5540 displayed much higher (+)-γ-lactamase activity than any other biochemically characterized (+)-γ-lactamases. Overall, we discovered a novel (+)-γ-lactamase Mh33H4-5540 which displayed the highest activity. It could be a promising candidate of biocatalyst for industrial applications of highly valuable chiral pharmaceutical chemicals.

The enantiomers of 2-azabicyclo[2.2.1]hept-5-en-3-one (γ-lactam) are key chiral synthons in the synthesis of antiviral drugs such as carbovir and abacavir. (+)-γ-Lactamase can be used as a catalyst in the enzymatic preparation of optically pure (−)-γ-lactam. Here, a (+)-γ-lactamase discovered from Bradyrhizobium japonicum USDA 6 by sequence-structure guided genome mining was cloned, purified and characterized. The enzyme possesses a significant catalytic activity towards γ-lactam. The active site of the (+)-γ-lactamase was studied by homologous modeling and molecular docking, and the accuracy of the prediction was confirmed by site-specific mutagenesis. The (+)-γ-lactamase reveals the great practical potential as an enzymatic method for the efficient production of carbocyclic nucleosides of pharmaceutical interest.Synthesis of the intermediate of abacavir and carbovir using a novel (+)-γ-lactamase.

A thermostable formamidase from the aerobic hyperthermophilic archaeon Aeropyrum pernix was revealed a novel type II (+)-γ-lactamase. This type II (+)-γ-lactamase is only composed of 377 amino acid residues, in contrast to another thermostable (+)-γ-lactamase from Sulfolobus solfataricus with 504 amino acid residues (type I). It is interesting that there are low identities between these two (+)-γ-lactamases, and herein, we further proved that at least two types of (+)-γ-lactamases exist in nature due to enzyme promiscuity. The gene of this thermostable (+)-γ-lactamase was cloned, functionally expressed in Escherichia coli BL21, and purified by a simple yet effective heat treatment method. It showed incredible thermostability, retaining 100 % of its activity after 12 h at 100 °C. The optimum temperature for this enzyme was supposed to be more than 100 °C, and the optimum pH for this enzyme was about 9.0. The lactamase maintained its activity in the presence of most metal ions, except for Cu2+. This thermo- and alkaline-tolerant (+)-γ-lactamase presents promising properties for the industrial application. Specifically, it could be used for the production of chirally pure (−)-γ-lactam for the synthesis of well-known carbocyclic nucleosides like abacavir and peramivir. The optical purity of the chiral product reached over 97 % enantiomeric excess.

Whole cells of Bradyrhizobium japonicum USDA 6 showed both (+)-γ-lactamase activity and (−)-γ-lactamase activity. Insight into the genome of B. japonicum USDA 6 revealed two potential γ-lactamases: a type I (+)-γ-lactamase and a (−)-γ-lactamase, making it the first strain to contain two totally different enantioselective lactamases. Both recombinant enzymes could easily be used to prepare either optically pure (+)-γ-lactam ((+)-2-azabicyclo[2.2.1]hept-5-en-3-one) or optically pure (−)-γ-lactam ((−)-2-azabicyclo[2.2.1]hept-5-en-3-one), which are versatile synthetic building blocks for the synthesis of various carbocyclic nucleosides and carbocyclic sugar analogues. Bioinformatic analysis showed that the type I (+)-γ-lactamase belongs to the amidase signature family, with 504 amino acids; the (−)-γ-lactamase, which consists of 274 amino acids, belongs to the hydrolase family. Here, we report that B. japonicum USDA contains a (−)-γ-lactamase in addition to a (+)-γ-lactamase, and it is the (−)-γ-lactamase from this strain that is examined in detail in this Letter. Enzymatic synthesis of optically pure (+)-γ-lactam with nearly 50% isolated yield and >99% ee was achieved.

•Homology model of a novel (+) gamma-lactamase was constructed and refined.•The specific substrate (+) gamma-lactam was docked into the active site.•The active site, binding pocket, and key residues of BjGL were identified.•A potential mechanism of (+) gamma-lactam hydrolysis was proposed.(+) Gamma-lactamases are enantioselective hydrolysis enzymes that can be used to produce optically pure (−) gamma-lactam, an important pharmaceutical intermediate for the anti-AIDS drug Abacavir. In this study, homology modeling and molecular dynamic simulation studies of a 3D homology model of BjGL, a novel (+) gamma-lactamase from Bradyrhizobium japonicum, were constructed and refined. The specific substrate (+) gamma-lactam and its enantiomer (−) gamma-lactam which can not be hydrolyzed was docked into the active site respectively, and the catalytic triad and other crucial residues that participate in the formation of the hydrophobic binding pocket, hydrogen bonds, and the oxyanion hole were identified. Furthermore, possible reasons for the high diastereoselectivity of BjGL binding with the substrate are proposed.

Biocatalyzed synthesis of nucleoside analogues was carried out using two thermostable nucleoside phosphorylases from the hyperthermophilic aerobic crenarchaeon Aeropyrum pernix K1. The synthesis of the 2,6-diaminopurine nucleoside and 5-methyluridine was used as a reaction model to test the process. Both the purine nucleoside phosphorylase (apPNP) and uridine phosphorylase (apUP) were functionally expressed in Escherichia coli. The recombinant enzymes were characterized after purification, and both enzymes showed high thermostability and broad substrate specificity. Both enzymes retained 100 % of their activity after 60 min at high temperature, and the optimum temperature for the enzymes was 90–100 °C. The nucleoside phosphorylases obtained from A. pernix are valuable industrial biocatalysts for high-temperature reactions that produce nucleoside drugs in high yields.

5-Methyluridine has been synthesized in high yield using guanosine and thymine as starting materials in the presence of highly thermostable recombinant purine nucleoside phosphorylase (PNP) and uridine phosphorylase (UP) obtained from hyperthermophilic aerobic crenarchaeon Aeropyrum pernix. Key reaction parameters such as pH, temperature, concentration of buffer and substrates were investigated. At the optimal conditions, 5-methyluridine was achieved in yield 85% with a guanosine conversion of 96% in 10 ml scale. The process can be performed at high temperature, which will highly increase the solubility of substrates, therefore, this process is suitable for the industry application.

A (−)γ-lactamase, Mhg, from Microbacterium hydrocarbonoxydans was over-expressed in E. coli and was characterized after purification. The maximum activity was at pH 8.0 and 60°C and the half life of Mhg was ~30 min at 75°C. The enzyme was activated by DTT. The catalytic triad of the (−)γ-lactamase is comprised of residues Ser98, Asp230, and His259 and an oxyanion hole was formed by Tyr32 and Met99 according to the alignment results. Under native conditions, the (−)γ-lactamase consists of two 31 kDa homodimers.

An esterase, Sso2518, from Sulfolobus solfataricus P2 was over-expressed in E. coli. and characterized after purification. The maximum activity was at pH 7.5 and 50°C. The half life of Sso2518 was about 30 min at 85°C and the enzyme was activated by Cu2+. The catalytic triad of Sso2518 was comprised of residues Ser151, Asp176, and His328. Sso2518 showed the highest activity with p-nitrophenyl caproate (C6) and could also hydrolyze olive oil. Under native conditions, Sso2518 consists of 125 kDa homotrimers.

Using immobilized cells of a novel strain of Microbacterium hydrocarbonoxydans L29-9 in polymers of polyvinyl alcohol (PVA)–alginate–boric acid, enantioselective resolution of racemic γ-lactam to produce (−)γ-lactam was successfully carried out. A 6:1 ratio of PVA:sodium alginate not only prevented agglomeration of the matrix but also produced beads with high gel strength. The optimum biotransformation conditions were 1 g/L substrate, pH 7.0, reaction temperature of 30 °C, and reaction time of 3 h. After every two cycles, the immobilized cell beads were separated and immersed in 0.5 mM KCl solution at 4 °C for preservation. At optimum conditions, the enantiomeric excess and the yield of (−)γ-lactam were >99% and 34%, respectively. The beads showed a slight decrease in the enantiomeric excess when re-used up to 14 cycles (the enantioselectivity of the immobilized cells decreased slightly after 14 cycles of usage).

An esterase from Bacillus cereus that hydrolyzes 1-chloro-3-(1-napthyloxy)-2-acetoxypropanol was purified to homogeneity. After purification, the molecular mass of the esterase was determined as 43 kDa by SDS-PAGE, and estimated as 45 kDa using gel filtration, suggesting that the enzyme is a monomer. The optimum pH and temperature for activity of the enzyme were 7.0 and 40°C respectively. The N-terminal sequence was determined. Whole cells of this strain were applied to the resolution of 1-chloro-3-(1-napthyloxy)-2-acetoxypropanol.

A (−) gamma-lactamase fromMicrobacterium hydrocarbonoxydans was purified to homogeneity by chromatography methods. SDS-PAGE showed the molecular weight of the enzyme was about 31 kDa. The purified enzyme had a specific activity of 61.3±2.5 U mg−1 for 2-azabicyclo [2.2.1] hept-5-en-3-one [(−) gamma-lactam]. The enantioselectivity factor (E) of the purified enzyme was 9.5±0.8 for unreacted (+) gamma-lactam. TheKm andVmax value were 2.3±0.2 mM and 80.0±15.4 U mg−1 respectively. The highest activity was found at 30 °C and pH 8.0. ESIMS mass spectrometry analysis results and N-terminal sequence indicated the (−) gamma-lactamase might be a new enzyme.

A thermostable formamidase from the hyperthermophilic archaeon Sulfolobus solfataricus P2 was revealed to be a novel, thermostable (+)-γ-lactamase. This (+)-γ-lactamase (Sso2810) is composed of only 318 amino acid residues, in contrast to a previously reported (+)-γ-lactamase (Sso2122) with 504 amino acid residues from the same strain. Herein, we demonstrate that a single strain may contain diverse (+)-γ-lactamases. The gene of this thermostable (+)-γ-lactamase was cloned, functionally expressed in Escherichia coli BL21 and purified by a simple yet effective heat treatment method. Sso2810 was biochemically characterized and compared to Sso2122, with phylogenetic analysis indicating different evolutionary histories for the two encoding genes. This newly found thermostable enzyme shows promising properties for industrial applications; specifically, it could be used for the production of chirally pure (−)-γ-lactam for the synthesis of well-known carbocyclic nucleoside antiretroviral agents like Abacavir and Peramivir. The chiral product of the enzyme was purified to >99% enantiomeric excess.

•A new type of epoxy graphene oxide was used as carrier for enzyme immobilization for the first time.•The range of pH tolerance increased from pH 8.0–9.0 to pH 4.0–10.0 after immobilization.•Reusability assay demonstrated that 70% of the enzyme activity remained after 15 repeated batch experiments.In this article, a new type of graphene oxide material was obtained by modification with epoxy chloropropane, which was used for the (+) γ-lactamase immobilization research. The enzymatic properties of the immobilized (+) γ-lactamase were systematically tested and compared with those of the free enzyme. The free and immobilized enzymes have the same optimum temperature (80 °C) and pH (8.0), the range of pH tolerance increased from pH 8.0–9.0 to pH 4.0–10.0 after immobilization, and the immobilized enzyme is less tolerant to heat than the free enzyme. Kinetic experiments showed that the Km value of the immobilized enzyme was about 2.66 times higher than that of the free enzyme, whereas Vmax decreased 40%. Subsequently, the apparent activation energies (Ea) of the free and immobilized enzymes became 40.03 and 35.62 kJ/mol, respectively. Finally, a reusability assay demonstrated that 70% of the enzyme activity remained after 15 repeated batch experiments.The schematic representation is our main research. In this paper, we prepared a new type of graphene oxide material through modification with epoxy chloropropane, which was used for the (+) γ-lactamase immobilization research.Download full-size image