A new type of AmpC β-lactamases defined by PIB-1, a metal-dependent carbapenem-hydrolyzing β-lactamase, from Pseudomonas aeruginosa : structural and functional analysis

Antibiotic resistance is one of most important health concerns nowadays. β-lactamases are the most important resistance determinants. Based on their structural and functional characteristics β-lactamases are grouped in four categories. AmpC β-lactamases are cephalosporinases presenting a set of highly conserved residues. Here we crystallized PIB-1, a Pseudomonas aeruginosa chromosomally-encoded β-lactamase. Its crystal structure shows it is an AmpC β-lactamase, although the number of conserved residues is low. Functional analysis showed that PIB-1 is able to degrade carbapenems but not the typical substrate of AmpC β-lactamases, cephalosporins. Besides, the catalytic activity of PIB-1 increases in the presence of metal ions. Metals do not bind to the active center and increase the degradation of the antibiotic. They induce the formation of trimers. This suggests that the oligomer is more active than the monomer. While PIB-1 is structurally an AmpC β-lactamase, the low sequence conservation, substrate profile and its metal-dependence, prompts us to position this enzyme as the founder of a new group inside the AmpC β-lactamases. Consequently, the diversity of AmpC β-lactamases might be wider than expected.