The fluoride permeation pathway and anion recognition in Fluc family fluoride channels

Abstract
Data availability
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Abstract

Fluc family fluoride channels protect microbes against ambient environmental fluoride by undermining the cytoplasmic accumulation of this toxic halide. These proteins are structurally idiosyncratic, and thus the permeation pathway and mechanism have no analogy in other known ion channels. Although fluoride binding sites were identified in previous structural studies, it was not evident how these ions access aqueous solution, and the molecular determinants of anion recognition and selectivity have not been elucidated. Using x-ray crystallography, planar bilayer electrophysiology and liposome-based assays, we identify additional binding sites along the permeation pathway. We use this information to develop an oriented system for planar lipid bilayer electrophysiology and observe anion block at one of these sites, revealing insights into the mechanism of anion recognition. We propose a permeation mechanism involving alternating occupancy of anion binding sites that are fully assembled only as the substrate approaches.

Data availability

Atomic coordinates for the Fluc-Ec2 and mutants in the presence of Br- have been deposited in the Protein Data Bank under accession numbers 7KKR (WT); 7KKA (S81A); 7KKB (S81C); 7KK8 (S81T); 7KK9 (S81A/T81A). Source data files have been provided for all figures. No custom code was used.

Article and author information

Author details

Benjamin C McIlwain

Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States

Competing interests
No competing interests declared.
Roja Gundepudi

Program in Biophysics, University of Michigan, Ann Arbor, MI, United States

Competing interests
No competing interests declared.
B Ben Koff

Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States

Competing interests
No competing interests declared.
Randy B Stockbridge

Molecular, Cellular, and Developmental Biology and Program in Biophysics, University of Michigan, Ann Arbor, MI, United States

For correspondence
stockbr@umich.edu

Competing interests
Randy B Stockbridge, Reviewing editor, eLife.

"This ORCID iD identifies the author of this article:" 0000-0001-8848-3032

Funding

National Institutes of Health (R35-GM128768)

Randy B Stockbridge

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Copyright

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.