Referenced in: none

Automatically associated channels: Slo1

Title: Structure-kinetic relationship of carbapenem antibacterials permeating through E. coli OmpC porin.

Authors: Que-Tien Tran, Robert A Pearlstein, Sarah Williams, John Reilly, Thomas Krucker, Gül Erdemli

Journal, date & volume: Proteins, 2014 Nov , 82, 2998-3012

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/25082756

Abstract
The emergence of Gram-negative "superbugs" exhibiting resistance to known antibacterials poses a major public health concern. Low molecular weight Gram-negative antibacterials are believed to penetrate the outer bacterial membrane (OM) through porin channels. Therefore, intracellular exposure needed to drive antibacterial target occupancy should depend critically on the translocation rates through these proteins and avoidance of efflux pumps. We used electrophysiology to study the structure-translocation kinetics relationships of a set of carbapenem antibacterials through purified porin OmpC reconstituted in phospholipid bilayers. We also studied the relative susceptibility of OmpC+ and OmpC- E. coli to these compounds as an orthogonal test of translocation. Carbapenems exhibit good efficacy in OmpC-expressing E. coli cells compared with other known antibacterials. Ertapenem, which contains an additional acidic group compared to other analogs, exhibits the fastest entry into OmpC (k(on) ≈ 2 × 10(4) M(-1) s(-1)). Zwitterionic compounds with highly polar groups attached to the penem-2 ring, including panipenem, imipenem and doripenem exhibit faster k(on) (>10(4) M(-1) s(-1)), while meropenem and biapenem with fewer exposed polar groups exhibit slower k(on) (∼5 × 10(3) M(-1) s(-1)). Tebipenem pivoxil and razupenem exhibit ∼13-fold slower k(on) (∼1.5 × 10(3) M(-1) s(-1)) than ertapenem. Overall, our results suggest that (a) OmpC serves as an important route of entry of these antibacterials into E. coli cells; and (b) that the structure-kinetic relationships of carbapenem translocation are governed by H-bond acceptor/donor composition (in accordance with our previous findings that the enthalpic cost of transferring water from the constriction zone to bulk solvent increases in the presence of exposed nonpolar groups).