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Structures of the Otopetrin Proton Channels Otop1 and Otop3

By Kei Saotome, Bochuan Teng, Che Chun (Alex) Tsui, Wen-Hsin Lee, Yu-Hsiang Tu, Mark S. P. Sansom, Emily R. Liman, Andrew B. Ward

Posted 06 Feb 2019
bioRxiv DOI: 10.1101/542308 (published DOI: 10.1038/s41594-019-0235-9)

Otopetrins (Otop1-Otop3) comprise one of only two known eukaryotic proton-selective channel families. Otop1 is required for formation of otoconia and is a candidate mammalian sour taste receptor. Here, we report cryo-EM structures of zebrafish Otop1 and chicken Otop3 in lipid nanodiscs. The structures reveal a dimeric architecture of Otopetrins with each subunit consisting of twelve transmembrane helices divided into structurally related N and C domains. Cholesterol-like molecules occupy various sites in Otop1 and Otop3 and occlude a cavernous central tunnel. Two hydrophilic vestibules, as well as the intrasubunit interface between N and C domains, form conduits for water entry into the membrane plane in molecular dynamics simulations, suggesting they each could provide pathways for proton conduction. We also demonstrate the functional relevance of a salt bridge in the C domain vestibule by mutagenesis. Our results provide a structural basis for understanding the function of the Otopetrin proton channel family.

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