Uncovering the Mechanism of the Proton-Coupled Fluoride Transport in the CLC Antiporter.

Fluoride is a natural antibiotic abundantly present in the environment and, in micromolar concentrations, is able to inhibit enzymes necessary for bacteria to survive. However, as is the case with many antibiotics, bacteria have evolved resistance methods, including through the use of recently discovered membrane proteins. One such protein is the CLC F/H antiporter protein, a member of the CLC superfamily of anion-transport proteins. Though previous studies have examined this F transporter, many questions are still left unanswered. To reveal details of the transport mechanism used by CLC, we have employed molecular dynamics simulations and umbrella sampling calculations. Our results have led to several discoveries, including the mechanism of proton import and how it is able to aid in the fluoride export. Additionally, we have determined the role of the previously identified residues Glu118, Glu318, Met79, and Tyr396. This work is among the first studies of the CLC F/H antiporter and is the first computational investigation to model the full transport process, proposing a mechanism which couples the F export with the H import.