STRUCTURE OF CARB-4 AND AER-1 CARBENICILLIN-HYDROLYZING BETA-LACTAMASES

We determined the nucleotide sequences of bla(CARB-4) encoding CARE-4 and deduced a polypeptide of 288 amino acids. The gene was characteriz ed 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 th e bla genes for these beta-lactamases varied from 98.7 to 99,9%, while that between these genes and bla(CARB-4) encoding CARE-4 was 86,3%, T he bla(CARB-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 bla(AER-1) shared 60.8% DNA identity with bla(PSE-3) encoding PSE-3, The deduced AER-1 beta-lactamase peptide was compared to class A, B, C, and D enzy mes and had 57.6% identity with PSE-3, including an STHK tetrad at the active site. For CARE-I and AER-1, conserved canonical amino acid box es typical of class A beta-lactamases were identified in a multiple al ignment. Analysis of the DNA sequences flanking bla(CARB-4) and bla(AE R-1) confirmed the importance of gene cassettes acquired via integrons in bin gene distribution.