Antibiotic efflux is one of the most important mechanisms of bacterial multi-drug resistance. Antibiotics are pumped out of the bacterial cell by tripartite efflux pumps that are assembled from outer-membrane, periplasmic, and inner-membrane protein components. To date, the high-resolution structure of an entire efflux pump complex has remained elusive. Our efforts have focused on filling this gap by combining data from various experimental techniques with the available crystal structure and cryo-EM data to develop computational methods to construct atomic-level resolution models of the full efflux pump complex. Then, we use these models of entire efflux pump complex in a gram-negative membrane mimic with inner and outer membranes and periplasm.  We consider both all-atom and coarse-grained simulations to characterize the assembly of efflux pump and the free energy profile of the drug translocation. Our results suggest that the drug translocation depends on the size of the molecule. While drugs with varying sizes enter through a vestibule accessible from periplasm, only smaller drugs can enter the pump through a channel from the cytoplasmic leaflet of the inner-membrane component. Overall, drug binding leads to subtle conformational changes that are transmitted along the components in the periplasmic region. The influence of such drug induced conformational changes on the periplasmic and outer-membrane components and the coupling to the proton motive force are also being probed. These molecular level findings are integrated into a mechanistic kinetic model of antibiotic efflux for quantitative comparison with measurements.<br/>

Assembly and mechanistic details of drug translocation in MexAB-OprM efflux pump

249th National Meeting (2015)

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