Antibiotic Transport through Porins

The emergence and dissemination of coordinated resistance mechanism (MDR) underline the importance to understand the rate limiting steps in antibiotic action. Here OmpF porin from E. coli is used as an example to demonstrate what limits the penetration of carbapenems. Bacteriological kinetic killing assays, temperature dependent ion conductance measurements, and all-atom computer simulations were combined to study interaction and translocation of clinically relevant β-lactam antibiotics through wild type OmpF and two mutants D113A and D121A, where the key residues at the constriction region have been substituted. Expression of these various OmpF mutants in an otherwise porin-null bacterial strain revealed an increase of bacterial susceptibility for the mutants. High-resolution conductance measurements and modulating the temperature indicates lower energy barriers for mutant porin correlating with the microbiological assays. All atom modeling provided a most probable pathway able to identify the relevant side-chain interactions. This combined approach allows identifying rate limiting interaction and suggests possible modification to enhance antibiotic penetration.References:1. Hajjar E, et al. Bridging timescales and length scales: from macroscopic flux to molecular mechanism of antibiotic diffusion through porins. Biophys J. 2010, 98, 569-75.2. Singh PR, et al. Antibiotic permeation across the OmpF channel: modulation of the affinity site in the presence of magnesium. J Phys Chem B. 2012, 116, 4433-8.