Structure and kinetics of the beta-lactamase mutants S70A and K73H from Staphylococcus aureus PC1

Two mutant beta-lactamases from Staphylococcus aureus PC1 which probe key catalytic residues were formed by site-directed mutagenesis. The nucleophilic group that attacks the beta-lactam carbonyl carbon atom was removed in the S70A enzyme. The crystal structure of S70A beta-lactamase was determined at 2.1 angstrom resolution. The structure is similar to that of the native enzyme except for the mutation site. The K73H beta-lactamase was tested for the possible role of Lys73 in proton transfer. It did not show any activity toward benzylpenicillin. The crystal structure of K73H beta-lactamase was determined at 1.9 angstrom resolution.