β-xylosidases (4-β-d-xylan xylohydrolase, E.C. 3.2.1.37) are glycoside hydrolases (GH) catalyzing the hydrolysis of (1→4)-β-d-xylans, allowing for the removal of β-d-xylose residues from its non-reducing termini. Together with other xylan-degrading enzymes, β-xylosidases are involved in the enzymatic hydrolysis of lignocellulosic biomass, making them highly valuable in the biotechnological field. Whereas different GH families are deeply characterized from a structural point of view, the GH52 family has been barely described. In this work, we report the 2.25 Å resolution structure of Geobacillus stearothermophilus CECT43 XynB2, providing the second structural characterization for this GH family. A plausible dynamic loop closing the entrance of the catalytic cleft is proposed based on the comparison of the available GH52 structures, suggesting the relevance of a dimeric structure for members of this family. The glycone specificity at the −1 site for GH52 and GH116 members is also explained by our structural studies.
