The structure of OmpF porin in complex with three common antibiotics
(zwitterionic ampicillin, anionic ertapenem, and di-anionic carbenicillin) was
determined using X-ray crystallography. The three antibiotics are found to bind
within the extracellular and periplasmic pore vestibules, away from the narrow
OmpF constriction zone. Using the X-ray structures as a starting point,
nonequilibrium molecular dynamics simulations with an applied membrane voltage
show that ionic current through the OmpF channel is blocked with bound
ampicillin, but not with bound carbenicillin. The susceptibility of Escherichia
coli expressing OmpF mutants to ampicillin and carbenicillin was also
experimentally characterized using microbiologic assays. These results show that
general diffusion by OmpF porins allows for transfer of molecules with varied
charged states and give insights into the design of more efficient antibiotics.
A better understanding of this mechanism will shed light on nature's way of
devising channels able to enhance the transport of molecules through membranes.
