title: Amino acid sequence determinants of extended spectrum cephalosporin hydrolysis by the class C P99 beta-lactamase.
abstract: Class C beta-lactamases are commonly encoded on the chromosome of Gram-negative bacterial species. Mutations leading to increased expression of these enzymes are a common cause of resistance to many cephalosporins including extended spectrum cephalosporins. Recent reports of plasmid- and integrin-encoded class C beta-lactamases are a cause for concern because these enzymes are likely to spread horizontally to susceptible strains. Because of their increasing clinical significance, it is critical to identify the determinants of catalysis and substrate specificity of these enzymes. For this purpose, the codons of a set of 21 amino acid residues that encompass the active site region of the P99 beta-lactamase were individually randomized to create libraries containing all possible amino acid substitutions. The amino acid sequence requirements for the hydrolysis of ceftazidime, an extended spectrum cephalosporin commonly used to treat serious infections, were determined by selecting resistant mutants from each of the 21 libraries. DNA sequencing identified the residue positions that are critical for ceftazidime hydrolysis. In addition, it was found that certain amino acid substitutions in the omega-loop region of the P99 enzyme result in increased ceftazidime hydrolysis suggesting the loop is an important determinant of substrate specificity.
authors.affiliation: Structural and Computational Biology and Molecular Biophysics Program, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Zhang
authors.forename: Y
authors.initials: Y
authors.lastname: Yu
authors.forename: J M
authors.initials: JM
authors.lastname: Musser
authors.forename: T
authors.initials: T
authors.lastname: Palzkill
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D002511:Cephalosporins / Q000378:metabolism*; D017931:DNA Primers; D006868:Hydrolysis; D008958:Models, Molecular; D008969:Molecular Sequence Data; D001618:beta-Lactamases / Q000737:chemistry / Q000378:metabolism*
chemical_list: D002511:Cephalosporins; D017931:DNA Primers; D001618:beta-Lactamases