Glutamic acid 160 is the acid-base catalyst of beta-xylosidase from Bacillus stearothermophilus T-6: a family 39 glycoside hydrolase

A beta -xylosidase from Bacillus stearothermophilus T-6 was cloned, overexp ressed in Escherichia coli and purified to homogencity. Based on sequence a lignment, the enzyme belongs to family 39 glycoside hydrolases, which itsel f forms part of the wider GH-A dan. The conserved Glu160 rr:as proposed as the acid-base catalyst. An E160A mutant was constructed and subjected to st eady state and pre-steady state kinetic analysis together with azide rescue and pll activity profiles. The observed results support the assignment of Glu160 as the acid-base catalytic residue. (C) 2001 Published by Elsevier S cience B.V, on behalf of the Federation of European Biochemical Societies.