He_2025_Front.Microbiol_16_1662394

Extremozymes from Antarctic microbiota represent a potential source of unique biocatalysts. In this study, a novel esterase gene est2 was identified from the Antarctic bacterium Pseudomonas sp. A6-5. Phylogenetic and sequence analyses classified it as the founding member of a new esterase family XXII. The catalytic triad of the enzyme consisted of Ser(141), Asp(275), and His(303), with the nucleophilic Ser(141) situated within the characteristic GXSXG motif of alpha/beta-hydrolases. Est2 exhibited remarkable cold-adaptation where 20-85% of the maximum activity was observed at temperatures ranging from 0 to 15 degreesC. Substrate specificity profiling revealed preferential hydrolysis of medium-chain p-nitrophenyl esters and triglyceride emulsions. Enzyme activity was sensitive to inhibition by transition metals (1 mM of Mn(2+), Cu(2+), Co(2+), Ni(2+) or Zn(2+)), but alkali metals were considerably less effective. Representative polar-protic and -aprotic solvents uniformly inhibited Est2 activity. Collectively, these results suggest the structural stability of Est2 is largely governed by hydrophobic interactions and H-bonding, rather than ionic forces. Est2 appears to represent a unique cold-adaptive enzyme that may be suitable for bio-catalyzed environmental remediation.