High-Throughput Crystallography Reveals Boron-Containing Inhibitors of a Penicillin-Binding Protein with Di- and Tricovalent Binding Modes

The effectiveness
of β-lactam antibiotics is increasingly
compromised by β-lactamases. Boron-containing inhibitors are
potent serine-β-lactamase inhibitors, but the interactions of
boron-based compounds with the penicillin-binding protein (PBP) β-lactam
targets have not been extensively studied. We used high-throughput
X-ray crystallography to explore reactions of a boron-containing fragment
set with the Pseudomonas aeruginosa PBP3 (PaPBP3). Multiple crystal structures reveal that boronic acids
react with PBPs to give tricovalently linked complexes bonded to Ser294,
Ser349, and Lys484 of PaPBP3; benzoxaboroles react with PaPBP3 via
reaction with two nucleophilic serines (Ser294 and Ser349) to give
dicovalently linked complexes; and vaborbactam reacts to give a monocovalently
linked complex. Modifications of the benzoxaborole scaffold resulted
in a moderately potent inhibition of PaPBP3, though no antibacterial
activity was observed. Overall, the results further evidence the potential
for the development of new classes of boron-based antibiotics, which
are not compromised by β-lactamase-driven resistance.