Fluoride Action Network

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Abstract

The Chloride Channel (CLC) family includes proton-coupled chloride and fluoride transporters. Despite their similar protein architecture, the former exchange two chloride ions for each proton and are inhibited by fluoride, whereas the latter efficiently transport one fluoride in exchange for one proton. The combination of structural, mutagenesis, and functional experiments with molecular simulations has pinpointed several amino acid changes in the permeation pathway that capitalize on the different chemical properties of chloride and fluoride to fine-tune protein function. Here we summarize recent findings on fluoride inhibition and transport in the two prototypical members of the CLC family, the chloride/proton transporter from Escherichia coli (CLC-ec1) and the fluoride/proton transporter from Enterococcus casseliflavus (CLCF-eca).

1 Electronic Supplementary Material

Data S1

Further computational details of the simulations reviewed in the main text.

Keywords

Chloride transporters; CLC; CLCF; Electrophysiology; Fluoride transporters; Metadynamics; Molecular dynamics; Multiscale simulations; Mutagenesis; Quantum mechanics/molecular mechanics; X-ray crystallography

*Original abstract online at https://link.springer.com/chapter/10.1007/164_2022_593

Notes

1. Fluoride is isosteric with hydroxide and can compete with phosphate and carboxylate groups, thus acting as a substrate- or transition state-like inhibitor of several enzymatic reactions (Strunecka and Strunecky 2020).

2. Higher organisms can avoid fluoride’s harmful effects, thanks to the exquisite selectivity of most of their anion channels and transporters, which limits fluoride resorption in the gastrointestinal tract (Johnston and Strobel 2020).

3. Larger anions, such as nitrate and thiocyanate, can still be transported by CLC proteins, though with different selectivity (Accardi 2015).

4. CLCF-eca belongs to the so-called MV subclade, i.e. CLCF proteins that contain Met and Val in the central binding site, compared to members of the NT subclade, which bear Asn and Thr. The former exhibits higher selectivity for fluoride over chloride than the latter (Brammer et al. 2014).

5. Chloride occupancy of Scen in CLC-ec1 has been observed in the crystal structure of the E148Q mutant (Lim et al. 2013).

6. The structure of the two E318 CLCF-eca mutants could not be solved by X-ray crystallography.

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*Original abstract online at https://link.springer.com/chapter/10.1007/164_2022_593

 

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