The esterase B from Sphingobium sp. SM42 has the new de-arenethiolase activity against cephalosporin antibiotics

Re-sensitization of imipenem-resistant Pseudomonas aeruginosa and restoration of cephalosporins susceptibility in Enterobacteriaceae by recombinant Esterase B

Sphingobium sp. SM42 Esterase B (EstB) is an enzyme with a dual function in degrading dibutyl phthalate and catalyzing the cleavage of the C-S bond in C3-sidechains of the dihydrothiazine ring of cephalosporins, generating more active β-lactam derivatives. Global prokaryotic genome analysis revealed the existence of a gene identical to estB in Pseudomonas aeruginosa strain PS1 suggesting a horizontal gene transfer event involving estB. To investigate the effect of ectopic expression of EstB in the periplasm of P. aeruginosa and several Enterobacteriaceae on antibiotic susceptibility levels, plasmid, pEstB, carrying a recombinant EstB fused with the signal peptide from Escherichia coli outer membrane protein A (OmpA) for periplasmic localization was constructed. The expression of EstB in the periplasm of P. aeruginosa and the Enterobacteriaceae: E. coli, Klebsiella pneumoniae, and Salmonella enterica serovar Typhi, increased susceptibility to carbapenems and cephalosporins. EstB reversed the imipenem resistance of P. aeruginosa ΔmexS and restored the changes in susceptibility to cephalosporins conferred by the downregulation of the outer membrane proteins, OmpK35 and OmpK36, in K. pneumoniae ΔramR-ompK36 to wild-type level. The introduction of EstB to the periplasmic space of Gram-negative bacteria can increase carbapenem and cephalosporin susceptibility.

A novel carboxylesterase from Acinetobacter sp. JNU9335 for efficient biosynthesis of Edoxaban precursor with high substrate to catalyst ratio

A novel carboxylesterase AcEst1 was identified from Acinetobacter sp. JNU9335 with high efficiency in the biosynthesis of chiral precursor of Edoxaban through kinetic resolution of methyl 3-cyclohexene-1-carboxylate (CHCM). Sequence analysis revealed AcEst1 belongs to family IV of esterolytic enzymes and exhibits <40% identities with known carboxylesterases. The optimum pH and temperature of recombinant AcEst1 are 8.0 and 40 °C. Substrate spectrum analysis indicated that AcEst1 prefers substrates with short acyl and alcohol groups. AcEst1 was highly active in the hydrolysis of CHCM with k_cat of 1153 s^-1 and displayed high substrate tolerance. As much as 2.0 M (280 g·L^-1) CHCM could be enantioselectively hydrolyzed into (S)-CHCM by merely 0.08 g·L^-1AcEst1 with ee_s of >99% (S) and substrate to catalyst ratio (S/C) of 3500 g·g^-1. These results indicate that the novel AcEst1 is a promising biocatalyst in the synthesis of chiral carboxylic acids.

Cefoperazone induces esterase B expression by EstR and esterase B enhances cefoperazone activity at the periplasm

The occurrence of antibiotic resistance bacteria has become a major threat to public health. We have recently discovered a transcriptional activator that belongs to MarR family, EstR, and an esterase B (EstB) with a newly proposed de-arenethiolase activity from Sphingobium sp. SM42. De-arenethiolase activity involves the removal of the small aromatic side chain of cephalosporin antibiotics as an excellent leaving group by the enzymatic CS bond cleavage. Here, we report the regulation of estB through EstR as an activator in response to a third generation cephalosporin, cefoperazone, antibiotic. Cefoperazone induced the expression of estB in wild type Sphingobium sp., but not in the estR knockout strain, and the induction was restored in the complemented strain. Moreover, we revealed the importance of EstB localization in periplasm. Since EsB has the ability to inactivate selected β-lactam antibiotics in vitro, it is possible that the enzyme works at the periplasmic space of Gram negative bacteria similar to β-lactamases. EstB was genetically engineered by incorporating NlpA binding motif, or OmpA signal sequence, or SpyTag-SpyCatcher to the estB gene to mobilize it to different compartments of periplasm; inner membrane, outer membrane, and periplasmic space, respectively. Surprisingly, we found that Sphingobium sp. SM42 and E. coli expressing EstB at the periplasm were more sensitive to cefoperazone. The possible drug enhancement mechanism by enzyme was proposed. This work might lead to a novel strategy to tackle antibiotic resistance problem.