An engineered Staphylococcus aureus PC1 beta-lactamase that hydrolyses third-generation cephalosporins.

The beta-lactamase from Staphylococcus aureus PC1 has been cloned into an Escherichia coli vector for site-directed mutagenesis and high-level protein expression. A mutant enzyme has been produced in which Ala238 is replaced by a serine, and Ile239 is deleted (A238S:I239del). The engineered enzyme hydrolyses third-generation cephalosporins substantially more rapidly than the parental enzyme does, while hydrolysis of benzylpenicillin is slower with the mutant than with the wild-type and native enzymes. The mutant beta-lactamase has been crystallized and the structure determined and refined at 2.8 A resolution. The disposition of the beta-strand which forms the side of the active site is altered in comparison with the native S. aureus beta-lactamase structure, widening the active site cleft and providing space to accommodate the bulky side-chains of the third-generation cephalosporins.