Biochemical identification of the catalytic residues of a glycoside hydrolase family 120 β-xylosidase, involved in xylooligosaccharide metabolisation by gut bacteria

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Cecchini, Davide | Fauré, Régis | Laville, Elisabeth | Veronese, Gabrielle

Edité par CCSD ; Wiley -

In press. The β-xylosidase B from Bifidobacterium adolescentis ATCC15703 belongs to the newly characterized family 120 of glycoside hydrolases. In order to investigate its catalytic mechanism, an extensive kinetic study of the wild-type enzyme and mutants targeting the three highly conserved residues Asp393, Glu416 and Glu364 was performed. NMR analysis of the xyloside hydrolysis products, the change of the reaction rate-limiting step for the Glu416 mutants, the pH dependency of E416A activity and its chemical rescue allowed to demonstrate that this GH120 enzyme uses a retaining mechanism of glycoside hydrolysis, Glu416 playing the role of acid/base catalyst and Asp393 that of nucleophile.

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