An enzymatic process for the efficient asymmetric reduction of 3H‐indoles as well as 3H‐indole iodides was developed for the first time. Using a new imine reductase identified from Paenibacillus lactis (PlSIR), various chiral indolines were facilely synthesized in good yields and excellent enantiopurities (up to >99% ee) under mild reaction conditions.

A new member of the CYP116B subfamily-P450LaMO-was discovered in Labrenzia aggregata by genomic data mining. It was successfully overexpressed in Escherichia coli, purified, and subsequently characterized spectroscopically, and its catalytic properties were assessed. Substrate profiling of the P450LaMO revealed that it was a versatile catalyst, exhibiting hydroxylation and epoxidation activities as well as O-dealkylation and asymmetric sulfoxidation activities. Diverse compounds, including alkylbenzenes, aromatic bicyclic molecules, and terpenoids, were shown to be hydroxylated by P450LaMO. Such diverse catalytic activities are uncommon for the bacterial P450s, and the P450LaMO-mediated stereoselective hydroxylation of inactivated C-H bonds-ubiquitous and relatively unreactive in organic molecules-is particularly unusual. The self-sufficient nature of P450LaMO, coupled with its broad substrate range, highlights it as an ideal template for directed evolution towards various applications.

A recombinant carboxylesterase, cloned from Pseudomonas putida and designated as rPPE, is capable of catalyzing the bioresolution of racemic 2-acetoxy-2-(2'-chlorophenyl)acetate (rac-AcO-CPA) with excellent (S)-enantioselectivity. Semirational design of the enzyme showed that the W187H variant could increase the activity by ∼100-fold compared to the wild type (WT) enzyme. In this study, we performed all-atom molecular dynamics (MD) simulations of both apo-rPPE and rPPE in complex with (S)-AcO-CPA to gain insights into the origin of the increased catalysis in the W187H mutant. Our results show differential binding of (S)-AcO-CPA in the WT and W187H enzymes, especially the interactions of the substrate with the two active site residues Ser159 and His286. The replacement of Trp187 by His leads to considerable structural rearrangement in the active site of W187H. Unlike in the WT rPPE, the cap domain in the W187 mutant shows an open conformation in the simulations of both apo and substrate-bound enzymes. This open conformation exposes the catalytic triad to the solvent through a water accessible channel, which may facilitate the entry of the substrate and/or the exit of the product. Binding free energy calculations confirmed that the substrate binds more strongly in W187H than in WT. On the basis of these computational results, we further predicted that the mutations W187Y and D287G might also be able to increase the substrate binding and thus improve the enzyme's catalytic efficiency. Experimental binding and kinetic assays on W187Y and D287G show improved catalytic efficiency over WT, but not W187H. Contrary to our prediction, W187Y shows slightly decreased substrate binding coupled with a 100-fold increase in turnover rate, while in D287G the substrate binding is 8 times stronger but with a slightly reduced turnover rate. Our work provides important molecular-level insights into the binding of the (S)-AcO-CPA substrate to carboxylesterase rPPEs, which will help guide future development of more efficient rPPE variants.

bA novel nonheme chloroperoxidase (RhEst1), with promiscuous esterase activity for enantioselective hydrolysis of ethyl (S)-2,2-dimethylcyclopropanecarboxylate, was identified from a shotgun library of Rhodococcus sp. strain ECU1013. RhEst1 was overexpressed in Escherichia coli BL21(DE3), purified to homogeneity, and functionally characterized. Fingerprinting analysis revealed that RhEst1 prefers para-nitrophenyl (pNP) esters of short-chain acyl groups. pNP esters with a cyclic acyl moiety, especially that with a cyclobutanyl group, were also substrates for RhEst1. The K m values for methyl 2,2-dimethylcyclopropanecarboxylate (DmCpCm) and ethyl 2,2-dimethylcyclopropane carboxylate (DmCpCe) were 0.25 and 0.43 mM, respectively. RhEst1 could serve as an efficient hydrolase for the bioproduction of optically pure (S)-2,2-dimethyl cyclopropane carboxylic acid (DmCpCa), which is an important chiral building block for cilastatin. As much as 0.5 M DmCpCe was enantioselectively hydrolyzed into (S)-DmCpCa, with a molar yield of 47.8% and an enantiomeric excess (ee) of 97.5%, indicating an extremely high enantioselectivity (E ‫؍‬ 240) of this novel and unique biocatalyst for green manufacturing of highly valuable chiral chemicals.

Error-prone PCR and site-directed mutagenesis around substrate channel were employed for improving an esterase (RhEst1) activity towards Cilastatin building block. RhEst1A147I/V148F/G254A showed 20 times higher activity than the native enzyme in whole cell biotransformation.