Fluoride (F^-) is a ubiquitous environmental xenobiotic which inhibits two essential enzymes necessary for bacterial survival when its concentration approaches the toxic level (10-100 μM). In 2012, researchers discovered a riboswitch that turns on transcription for the previously unknown CLC^F F^-/H⁺ antiporter upon F^- binding. This F^-transporter belongs to the CLC superfamily of anion-transport proteins, most notably known for their Cl^-/H⁺ antiporters and Cl^- channels. Although there have been few studies examining this F^- transporter, many questions are still left unanswered. As such, my research involves the use of computational modeling to specifically study the bacterial CLC^F antiporter and discover details about its structure and mechanism of transport. Previous studies on the CLC Cl^-/H⁺ antiporter have shown the importance of central serine (Ser) and tyrosine (Tyr) residues in the formation of an intracellular gate, as well as an external glutamate (Glu) which serves as an extracellular gate and transfers a proton to an internal Glu. Crystal structures of CLC^F, however, show it lacks both the internal Glu and central Ser, instead possessing a central methionine (Met). To investigate the mechanism of CLC^F, I performed double bilayer simulations which elucidated the transport pathway utilized by this protein, and the importance of both the unique Met and external Glu in the gating of this pathway. This discovery aided in running umbrella sampling simulations which uncovered necessary residue motions for F^- export and provided new details in the proton transfer between the external Glu and an internal Glu unique to CLC^F.

Kira Mills

The University of Texas at Dallas

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