Molecular and Biochemical Analysis of AST-1, a Class A β-Lactamase from Nocardia asteroides Sensu Stricto

A β-lactamase gene was cloned from a Nocardia asteroides sensu stricto clinical isolate. A recombinant plasmid, pAST-1, expressed the β-lactamase AST-1 in Escherichia coli JM109. Its pI was 4.8, and its relative molecular mass was 31 kDa. E. coli JM109(pAST-1) was resistant to penicillins and narrow-spectrum cephalosporins. The β-lactamase AST-1 had a restricted hydrolytic activity spectrum. Its activity was partially inhibited by clavulanic acid but not by sulbactam and tazobactam. AST-1 is an Ambler class A β-lactamase sharing 65% amino acid identity with β-lactamase FAR-1, the most closely related enzyme.