Uncovering the Mechanism of the Proton-Coupled Fluoride Transport in the CLCF Antiporter

Abstract

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 CLCF F-/H+ antiporter protein, a member of the CLC superfamily of anion-transport proteins, most notably known for their ability to transport chloride ions. While it possesses many similarities to the other CLC proteins, it also differs in several key ways, and though previous studies have examined this F- transporter, many questions are still left unanswered. To reveal details of the transport mechanism used by CLCF, 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 computational studies of the CLCF F-/H+ antiporter and is the first to propose a mechanism which couples both the proton and anion transport.