title: Functional analysis of the active site of a metallo-beta-lactamase proliferating in Japan.
abstract: An R-plasmid-mediated metallo-beta-lactamase was found in Klebsiella pneumoniae DK4 isolated in Japan in 1991. The nucleotide sequence of its structural gene revealed that the beta-lactamase termed DK4 was identical to the IMP-1 metallo-beta-lactamase which was mediated by a chromosomal gene of Serratia marcescens TN9106 isolated in Japan in 1991 (E. Osano et al., Antimicrob. Agents Chemother. 38:71-78, 1994). The dose effect of DK4 beta-lactamase production on the resistance levels indicated a significant contribution of the enzyme to bacterial resistance to all the beta-lactams except monobactams. The enzymatic characteristics of the DK4 beta-lactamase and its kinetic parameters for nine beta-lactams were examined. The DK4 beta-lactamase was confirmed to contain 2 mol of zinc per mol of enzyme protein. The apoenzyme that lacked the two zincs was structurally unstable, and the activities of only 30% of the apoenzyme molecules could be restored by the addition of 1 mM zinc sulfate. The substitution of five conserved histidines (His28, His86, His88, His149, His210) and a cysteine (Cys168) for an alanine indicated that His86, His88, and His149 served as ligands to one of the zincs and that Cys168 played a role as a ligand to the second zinc. Both zinc molecules contribute to the enzymatic process. Mutant enzymes that lack only one of these retained some activity. Additionally, a conserved aspartic acid at position 90 was replaced by asparagine. This mutant enzyme showed an approximately 1,000 times lower k(cat) value for cephalothin than that of the wild-type enzyme but retained the two zincs even after dialysis against zinc-free buffer. The observed effect of pH on the activity suggested that Asp90 functions as a general base in the enzymatic process.
authors.affiliation: Division of Microbial Chemistry, Faculty of Pharmaceutical Sciences, Chiba University, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Haruta
authors.forename: H
authors.initials: H
authors.lastname: Yamaguchi
authors.forename: E T
authors.initials: ET
authors.lastname: Yamamoto
authors.forename: Y
authors.initials: Y
authors.lastname: Eriguchi
authors.forename: M
authors.initials: M
authors.lastname: Nukaga
authors.forename: K
authors.initials: K
authors.lastname: O'Hara
authors.forename: T
authors.initials: T
authors.lastname: Sawai
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001051:Apoenzymes / Q000378:metabolism; D001224:Aspartic Acid / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D003545:Cysteine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology; D006639:Histidine / Q000378:metabolism; D006801:Humans; D007564:Japan; D007700:Kinetics; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D008024:Ligands; D008826:Microbial Sensitivity Tests; D016297:Mutagenesis, Site-Directed; D015032:Zinc / Q000378:metabolism; D018440:beta-Lactam Resistance / Q000502:physiology*; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism*; D047090:beta-Lactams
chemical_list: D000900:Anti-Bacterial Agents; D001051:Apoenzymes; D008024:Ligands; D047090:beta-Lactams; D001224:Aspartic Acid; D006639:Histidine; C409201:beta-lactamase IMP-1; D001618:beta-Lactamases; D015032:Zinc; D003545:Cysteine