Chemical Structures and Transit Kinetics of Carbapenems Translocating Through E. Coli OmpC

Abstract

Previously, we proposed a novel mechanism of antibacterial translocation through the general diffusion porin OmpC in Gram-negative E. coli (Abstract 12-A-3857-BPS, 2668-Pos). Our proposed mechanism explains the observed rapid translocation of substrates capable of replacing the H-bonds of solvating water in the channel constriction zone upon evacuation of this water to bulk solvent. This hypothesis is based on previous work linking protein-ligand association and dissociation barriers in general to the costs of water transfer to/from binding sites. In the current study, we investigated a set of 8 carbapenems (including known drugs and antibacterials in development) for their structure-translocation kinetic relationships with OmpC using electrophysiology and microbiology methods. Taking into account the supporting electrophysiology and microbiology data, we demonstrated that these molecules likewise translocate through OmpC porin at rates that depend on their polar composition and H-bond replacement ability. The additional acidic group of ertapenem compared to other analogs promoted the highest entry rate into OmpC (kon ∼2x104 M-1s-1). Zwitterionic compounds with highly polar groups attached to the penem-2 ring (i.e. panipenem, imipenem and doripenem) exhibited faster kon (>104 M-1s-1), while those zwitterionic analogs with fewer exposed polar groups (i.e. meropenem and biapenem) exhibited slower kon (∼5x103 M-1s-1). Tebipenem pivoxil, a pro-dug developed for oral absorption, and razupenem with a change to thiazol-2-yl-thio moiety exhibited the slowest kon rates in to OmpC (∼1.5x103 M-1s-1) and also showed interaction with the phospholipid membrane. Our findings may help better understand the molecular mechanisms underlying antibiotic uptake through the outer membrane of Gram-negative bacteria, which is a key step in achieving antibiotic exposure and efficacy at intracellular targets.