Nucleotide sequence of the gene encoding the active-site serine β-lactamase from Streptomyces cacaoi

The gene encoding the extracellular active-site serine β-lactamase of Streptomyces cacaoi previously cloned into Streptomyces lividans, has the information for the synthesis of a 303 amino-acid precursor. The β-lactamase as excreted by the host S. lividans ML1, has a ragged amino-terminus, indicating either the presence of a leader peptidase of poor specificity or the action of an amino-peptidase. The deduced primary structure has been confirmed by amino acid sequencing of a 10-residue stretch at the amino terminus of the mature protein and an 8-residue stretch containing the active-site serine. The S. cacaoiβ-lactamase is highly homologous with the class A β-lactamases of Streptomyces albus G and Staphylococcus aureus of known three-dimensional structure. Amino acid alignments show that the S. cacaoiβ-lactamase essentially differs from these two latter enzymes by short insertions and deletions that do not affect the spatial disposition of the secondary structures.