title: Active-site residues of the transpeptidase domain of penicillin-binding protein 2 from Escherichia coli: similarity in catalytic mechanism to class A beta-lactamases.
abstract: By means of amino acid sequence alignment with class A beta-lactamases, the residues essential for the catalytic activity of the peptidoglycan transpeptidase of penicillin-binding protein 2 (PBP2) have been predicted to be Lys333, Asp447, and Lys544, in addition to the acylation site residue for the acyl-enzyme mechanism, Ser330. Accordingly, these residues were replaced by site-directed mutagenesis, and the resultant mutants were examined as to penicillin-binding activity and genetic complementation, which represent only the acylation step and the total reaction during transpeptidation, respectively. All the mutants at position 333 showed the complete loss of both the binding and complementation activities. Most of the mutants at position 447 retained the binding activity but lost the complementation activity, the exception being the D447E mutant, which retained both. The binding rates for various penicillins of the D447N mutant, which had lost the complementation activity, were almost identical to those of the wild type. The binding of the mutants at position 544 tended to require a higher penicillin concentration, and that of the K544H mutant required a lower pH. When the roles of the counterpart residues, Lys73, Glu166, and Lys234, in class A beta-lactamases were considered, the results suggested that Lys333 and Asp447 are essential for the acylation and acyl-transfer steps, respectively, and that Lys544 stabilizes the Michaelis complex through its side-chain positive charge.
authors.affiliation: Department of Agricultural Chemistry, University of Tokyo, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Adachi
authors.forename: M
authors.initials: M
authors.lastname: Ishiguro
authors.forename: S
authors.initials: S
authors.lastname: Imajoh
authors.forename: T
authors.initials: T
authors.lastname: Ohta
authors.forename: H
authors.initials: H
authors.lastname: Matsuzawa
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001483:Base Sequence; D001665:Binding Sites; D002352:Carrier Proteins; D002384:Catalysis; D004926:Escherichia coli / Q000737:chemistry*; D005816:Genetic Complementation Test; D006602:Hexosyltransferases / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000235:genetics; D002267:Muramoylpentapeptide Carboxypeptidase; D016297:Mutagenesis, Site-Directed; D046915:Penicillin-Binding Proteins; D010406:Penicillins / Q000378:metabolism; D010458:Peptidyl Transferases / Q000737:chemistry* / Q000235:genetics; D011485:Protein Binding; D012689:Sequence Homology, Nucleic Acid; D001618:beta-Lactamases / Q000737:chemistry / Q000145:classification* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D009097:Multienzyme Complexes; D046915:Penicillin-Binding Proteins; D010406:Penicillins; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase; D001618:beta-Lactamases