Sequence, molecular structure, and catalytic mechanism of four hypothetical tannases from Streptomyces sp. 303MFCol5.2

Tannase (EC 3.1.1.20) primarily catalyzes the hydrolysis of ester and depside bonds in tannin substrates, and has extensive applications in the fields of food and chemicals. In this study, four hypothetical tannase-encoding genes from Streptomyces sp. 303MFCol5.2 were cloned and expressed in Escherichia coli. Enzyme activity assays showed that SS-1 and SS-3 have tannase activity; SS-2, SS-3 and SS-4 have esterase activity. Sequence comparison showed that tannase and esterase have their distinctive conserved pentapeptide motif "Gly-X-Ser-X-Gly" and SerAsp-His catalytic triad. In addition, the size and shape of the substrate binding pocket may affect conformational changes during binding to the substrate, leading to changes in substrate specificity and catalytic properties. Specifically, SS-1 and SS-3 have larger substrate binding pockets compared to SS-2 and SS-4, which may be more favorable for substrate binding. This study will provide new insights into the analysis of tannase and esterase and lay a theoretical foundation for further research and application.