title: Sequence analysis and enzyme kinetics of the L2 serine beta-lactamase from Stenotrophomonas maltophilia.
abstract: The L2 serine active-site beta-lactamase from Stenotrophomonas maltophilia has been classified as a clavulanic acid-sensitive cephalosporinase. The gene encoding this enzyme from S. maltophilia 1275 IID has been cloned on a 3.3-kb fragment into pK18 under the control of a Ptac promoter to generate recombinant plasmid pUB5840; when expressed in Escherichia coli, this gene confers resistance to cephalosporins and penicillins. Sequence analysis has revealed an open reading frame (ORF) of 909 bp with a GC content of 71.6%, comparable to that of the L1 metallo-beta-lactamase gene (68.4%) from the same bacterium. The ORF encodes an unmodified protein of 303 amino acids with a predicted molecular mass of 31.5 kDa, accommodating a putative leader peptide of 27 amino acids. Comparison of the amino acid sequence with those of other beta-lactamases showed it to be most closely related (54% identity) to the BLA-A beta-lactamase from Yersinia enterocolitica. Sequence identity is most obvious near the STXK active-site motif and the SDN loop motif common to all serine active-site penicillinases. Sequences outside the conserved regions display low homology with comparable regions of other class A penicillinases. Kinetics of the enzyme from the cloned gene demonstrated an increase in activity with cefotaxime but markedly less activity with imipenem than previously reported. Hence, the S. maltophilia L2 beta-lactamase is an inducible Ambler class A beta-lactamase which would account for the sensitivity to clavulanic acid.
authors.affiliation: Bristol Centre for Antimicrobial Research and Evaluation, Department of Microbiology and Pathology, Medical School, University of Bristol, United Kingdom.
authors.forename: T R
authors.initials: TR
authors.lastname: Walsh
authors.forename: A P
authors.initials: AP
authors.lastname: MacGowan
authors.forename: P M
authors.initials: PM
authors.lastname: Bennett
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D006868:Hydrolysis; D007700:Kinetics; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D014974:Xanthomonas / Q000201:enzymology*; D001618:beta-Lactamases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D001618:beta-Lactamases