The bla gene of the cephamycin cluster of Streptomyces clavuligerus encodes a class A beta-lactamase of low enzymatic activity

A gene (bla) encoding a beta-lactamase is present in the cephamycin gene cluster of Streptomyces clavuligerus, the strain producing clavulanic acid and a beta-lactamase inhibitory protein, The bin gene is located 5.1 kb downstream from and in the opposite orientation to cefE, encoding the deacetoxycephalosporin C synthase, The bla gene encodes a 332-residue protein (M-r, 35,218), similar to other class A beta-lactamases produced by actinomycetes, Modification (to SDG) of the SDN conserved motif of class A beta-lactamases as well as of amino acids in otherwise conserved regions in the molecule may explain the low penicillinase and cephalosporinase activities of the protein, The beta-lactamase has been purified to homogeneity and found to bind [H-3] benzylpenicillin, a result reflecting a rate-limiting deacylation step. Nucleotide sequences homologous to bla were found in all tested cephamycin producers, but several other Streptomyces species which produce a beta-lactamase do not contain genes for beta-lactam antibiotic biosynthesis.