title: beta-lactamase I from Bacillus cereus. Structure and site-directed mutagenesis.
abstract: The sequence of the gene for beta-lactamase I from Bacillus cereus 569/H has been redetermined. Oligonucleotide-directed mutagenesis has been carried out, and the effects of the changes on the ampicillin-resistance of Escherichia coli TG1 expressing the mutant genes have been studied. Lysine-73, close to the active-site serine-70 and a highly-conserved residue, has been converted into arginine. This change had a large effect on activity, but did not abolish it. An even larger effect was found in the mutant in which glutamate-166 had been converted into glutamine; this had little or no activity. On the other hand, the conversion of glutamate-168 into aspartate gave fully active enzyme. Glutamate-166 is an invariant residue, but glutamate-168 is not. Alanine-123 has been replaced by cysteine, to give active enzyme; this change forms part of the plan to introduce a disulphide bond into the enzyme.
mesh_terms: D000668:Ampicillin Resistance / Q000235:genetics; D001409:Bacillus cereus / Q000201:enzymology* / Q000235:genetics; D001483:Base Sequence; D001665:Binding Sites; D004926:Escherichia coli / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D009844:Oligosaccharides / Q000096:biosynthesis; D010405:Penicillinase / Q000235:genetics*
chemical_list: D009844:Oligosaccharides; D010405:Penicillinase