Exploring sequence requirements for C3/C4 carboxylate recognition in the Pseudomonas aeruginosa cephalosporinase: Insights into plasticity of the AmpC β-lactamase

Class C β-lactamases (AmpC cephalosporinases) contribute significantly to β-lactam treatment failure of infections caused by the clinically relevant Gram-negative pathogen Pseudomonas aeruginosa. Despite years of study of these important β-lactamases, the structure-function relationships of this enzyme are not well understood. An understanding of structure-function relationships is crucial to the design of both substrates and enzyme inhibitors to achieve high affinity but escape hydrolysis. To this end, we examined a molecular model of a P. aeruginosa AmpC β-lactamase, PDC-3, in complex with a boronate inhibitor and generated alanine variants at three putative C3/C4 β-lactam carboxylate binding amino acids. A panel of nine penicillin and cephalosporin analog boronates was synthesized to serve as active site probes of the PDC-3 enzyme and the Arg349Ala variant. In conjunction with substrate susceptibility testing, these boronates reveal important features about the specificity of the P. aeruginosa AmpC enzyme. Namely, this β-lactamase maintains a high level of activity despite the substitution of C3/C4 β-lactam carboxylate recognition residues. Unlike class A serine β-lactamases, our work indicates that PDC-3 possesses a “binding region” rather than specific binding amino acids. The multiplicity of regions interacting with the C3/C4 carboxylate has implications for the evolution and resistance profile of this enzyme.