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.
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.
F
F
Sanschagrin
N
N
Bejaoui
R C
RC
Levesque
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