Ion permeation controlled by hydrophobic residues and proton binding in the proton-activated chloride channel

Ruiqi Cai; Jingfeng Tang; Xing-Zhen Chen

doi:10.1016/j.isci.2021.103395

Ion permeation controlled by hydrophobic residues and proton binding in the proton-activated chloride channel

iScience. 2021 Nov 1;24(12):103395. doi: 10.1016/j.isci.2021.103395. eCollection 2021 Dec 17.

Authors

Ruiqi Cai¹, Jingfeng Tang², Xing-Zhen Chen¹

Affiliations

¹ Department of Physiology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada.
² National "111" Center for Cellular Regulation and Molecular Pharmaceutics, Hubei University of Technology, Wuhan, Hubei 430086, China.

Abstract

Recently identified proton-activated chloride channel (PAC) contains two transmembrane helices (S1-S2) and is involved in lysosome function, hypoxia adaption, stroke, and carcinogenesis. Although a PAC structure was recently resolved, its gating and activation mechanisms remained largely unknown. By the two-electrode voltage clamp electrophysiology in Xenopus oocytes, we found that the hydrophobicity of site 304 at fenestrations, but not that of neighbor sites, is important for maintaining PAC at a closed state at pH 7.5. When activated at acidic pH, PAC activity significantly increased with the hydrophilicity of site 307 within S2, but not with that of neighbor sites, suggesting that 307 acts as an activation gate. We identified six conserved protonatable residues critical for proton-induced activation, consistent with structural studies. Our study depicted a scheme in which proton binding induces conformational changes from the W304-controlled closed state at fenestrations to an activated state controlled by activation gate I307 in helix S2.

Keywords: Cell biology; Molecular biology; Structural biology.