Mechanisms Underlying Proton Release in CLC-type F-/H+ Antiporters

Maria Gabriella Chiariello; Mercedes Alfonso-Prieto; Emiliano Ippoliti; Christoph Fahlke; Paolo Carloni

doi:10.1021/acs.jpclett.1c00361

Mechanisms Underlying Proton Release in CLC-type F^-/H⁺ Antiporters

J Phys Chem Lett. 2021 May 13;12(18):4415-4420. doi: 10.1021/acs.jpclett.1c00361. Epub 2021 May 5.

Authors

Maria Gabriella Chiariello^{1

2

3}, Mercedes Alfonso-Prieto^{1

4}, Emiliano Ippoliti^{1

3}, Christoph Fahlke², Paolo Carloni^{1

3

5

6}

Affiliations

¹ Institute for Advanced Simulation (IAS-5) and Institute of Neuroscience and Medicine (INM-9), Computational Biomedicine, Forschungszentrum Jülich, 52425 Jülich, Germany.
² Institute of Biological Information Processing (IBI-1), Molekular- und Zellphysiologie, Forschungszentrum Jülich, 52425 Jülich, Germany.
³ JARA-HPC, Forschungszentrum Jülich, 54245 Jülich, Germany.
⁴ Cécile and Oskar Vogt Institute for Brain Research, University Hospital Düsseldorf, Medical Faculty, Heinrich Heine University Düsseldorf, 40225 Düsseldorf, Germany.
⁵ Department of Physics, RWTH Aachen University, 52056 Aachen, Germany.
⁶ JARA Institute Molecular Neuroscience and Neuroimaging (INM-11), Forschungszentrum Jülich, 52425 Jülich, Germany.

PMID: 33950673
DOI: 10.1021/acs.jpclett.1c00361

Abstract

The CLC family of anion channels and transporters includes Cl^-/H⁺ exchangers (blocked by F^-) and F^-/H⁺ exchangers (or CLC^Fs). CLC^Fs contain a glutamate (E318) in the central anion-binding site that is absent in CLC Cl^-/H⁺ exchangers. The X-ray structure of the protein from Enterococcus casseliflavus (CLC^F-eca) shows that E318 tightly binds to F^- when the gating glutamate (E118; highly conserved in the CLC family) faces the extracellular medium. Here, we use classical and DFT-based QM/MM metadynamics simulations to investigate proton transfer and release by CLC^F-eca. After up to down movement of protonated E118, both glutamates combine with F^- to form a triad, from which protons and F^- anions are released as HF. Our results illustrate how glutamate insertion into the central anion-binding site of CLC^F-eca permits the release of H⁺ to the cytosol as HF, thus enabling a net 1:1 F^-/H⁺ stoichiometry.