Structure of CARB-4 and AER-1 carbenicillin-hydrolyzing beta-lactamases.
We determined the nucleotide sequences of blaCARB-4 encoding CARB-4 and deduced a polypeptide of 288 amino acids. The gene was characterized as a variant of group 2c carbenicillin-hydrolyzing beta-lactamases such as PSE-4, PSE-1, and CARB-3. The level of DNA homology between the bla genes for these beta-lactamases varied from 98.7 to 99.9%, while that between these genes and blaCARB-4 encoding CARB-4 was 86.3%. The blaCARB-4 gene was acquired from some other source because it has a G+C content of 39.1%, compared to a G+C content of 67% for typical Pseudomonas aeruginosa genes. DNA sequencing revealed that blaAER-1 shared 60.8% DNA identity with blaPSE-3 encoding PSE-3. The deduced AER-1 beta-lactamase peptide was compared to class A, B, C, and D enzymes and had 57.6% identity with PSE-3, including an STHK tetrad at the active site. For CARB-4 and AER-1, conserved canonical amino acid boxes typical of class A beta-lactamases were identified in a multiple alignment. Analysis of the DNA sequences flanking blaCARB-4 and blaAER-1 confirmed the importance of gene cassettes acquired via integrons in bla gene distribution.
Sanschagrin
F
F
Microbiologie Moléculaire et Génie des Protéines, Sciences de la Vie et de la Santé, Faculté de Médecine et Pavillon Charles-Eugène Marchand, Université Laval, Ste-Foy, Québec, Canada G1K 7P4.
Bejaoui
N
N
Levesque
R C
RC
D000595:Amino Acid Sequence; D001483:Base Sequence; D002228:Carbenicillin / Q000378:metabolism*; D008969:Molecular Sequence Data; D010406:Penicillins / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D001618:beta-Lactamases / Q000737:chemistry*
D010406:Penicillins; D001618:beta-Lactamases; D002228:Carbenicillin