Identification of novel esterases for the synthesis of sterically demanding chiral alcohols by sequence-structure guided genome mining

Discovery, characterization and mechanism of a Microbacterium esterase for key d-biotin chiral intermediate synthesis

Esterases are crucial biocatalysts in chiral compound synthesis. Herein, a novel esterase EstSIT01 belonging to family V was identified from Microbacterium chocolatum SIT101 through genome mining and phylogenetic analysis. EstSIT01 demonstrated remarkable efficiency in asymmetrically hydrolyzing meso-dimethyl ester [Dimethyl cis-1,3-Dibenzyl-2-imidazolidine-4,5-dicarboxyate], producing over 99% yield and 99% enantiomeric excess (e.e.) for (4S, 5R)-monomethyl ester, a crucial chiral intermediate during the synthesis of d-biotin. Notably, the recombinant E. coli expressing EstSIT01 exhibited over 40-fold higher activity than that of the wild strain. EstSIT01 displays a preference for short-chain p-NP esters. The optimal temperature and pH were 45 °C and 10.0, with Km and kcat values of 0.147 mmol/L and 5.808 s- 1, respectively. Molecular docking and MD simulations suggest that the high stereoselectivity for meso-diester may attribute to the narrow entrance tunnel and unique binding pocket structure. Collectively, EstSIT01 holds great potential for preparing chiral carboxylic acids and esters.

Target Discovery of Novel α-L-Rhamnosidases from Human Fecal Metagenome and Application for Biotransformation of Natural Flavonoid Glycosides

As a green and powerful tool, biocatalysis has emerged as a perfect alternative to traditional chemistry. The bottleneck during process development is discovery of novel enzymes with desired properties and independent intellectual property. Herein, we have successfully bioprospected three novel bacterial α-L-rhamnosidases from human fecal metagenome using a combinatorial strategy by high-throughput de novo sequencing combined with in silico searching for catalytic key motifs. All three novel α-L-rhamnosidases shared low sequence identities with reported (< 35%) and putative ones (< 57%) from public database. All three novel α-L-rhamnosidases were over-expressed as soluble form in Escherichia coli with high-level production. Furthermore, all three novel α-L-rhamnosidases hydrolyzed the synthetic substrate p-nitrophenyl α-L-rhamnopyranoside and natural flavonoid glycosides rutin and naringin with some excellent properties, such as high activity in acidic pH, high activity at low or high temperature, and good tolerance for alcohols and DMSO. Our findings would provide a convenient route for target discovery of the promising biocatalysts from the metagenomes for biotransformation and biosynthesis.

Esterases as stereoselective biocatalysts

Non-lypolitic esterases are carboxylester hydrolases with preference for the hydrolysis of water-soluble esters bearing short-chain acyl residues. The potential of esterases as enantioselective biocatalysts has enlarged in the last few years due to the progresses achieved in different areas, such as screening methodologies, overproduction of recombinant esterases, structural information useful for understanding the rational behind enantioselectivity, and efficient methods in protein engineering. Contributions of these complementary know-hows to the development of new robust enantioselective esterases are critically discussed in this review.