Structures of the otopetrin proton channels Otop1 and Otop3

Abstract

Otopetrins (Otop1–Otop3) comprise one of two known eukaryotic proton-selective channel families. Otop1 is required for otoconia formation and 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, with each subunit forming twelve transmembrane helices divided into structurally similar amino (N) and carboxy (C) domains. Cholesterol-like molecules occupy various sites in Otop1 and Otop3 and occlude a central tunnel. In molecular dynamics simulations, hydrophilic vestibules formed by the N and C domains and in the intrasubunit interface between N and C domains form conduits for water entry into the membrane core, suggesting three potential proton conduction pathways. By mutagenesis, we test the roles of charged residues in each putative permeation pathway. Our results provide a structural basis for understanding selective proton permeation and gating of this conserved family of proton channels.

Cellular and Neural Responses to Sour Stimuli Require the Proton Channel Otop1

“…In contrast, Otop1 is well established to function as a proton channel in heterologous cells [34]. Moreover, cryoelectron microscopy (cryo-EM) studies have revealed the structure of the Otop1 channel [58], allowing an understanding of how proton selectivity is achieved.…”

Relative Affinities of Protein-Cholesterol Interactions from Equilibrium Molecular Dynamics Simulations

“…In these instances, the bound density is either cholesterol, co-purified from the native bilayer 24–26 , or may correspond to cholesterol derivatives such as cholesterol-hemisuccinate (CHS), which are added during purification 27,28 . Often multiple cholesterol binding sites are observed within the same structure 25 . For example a recent structure of the serotonin receptor, 5-HT 1A (Protein Databank (PDB) ID: 7E2X), revealed 10 cholesterol molecules surrounding the TMD, including one partially buried cholesterol adjacent to the orthosteric ligand pocket 29 .…”

Transcription Factors of the Alx Family: Evolutionarily Conserved Regulators of Deuterostome Skeletogenesis

“…Sea urchin Alx1 also provides positive inputs directly into otop2L, the single sea urchin ortholog of the vertebrate otopetrin genes (Rafiq et al, 2014;Khor et al, 2019). Otopetrins are multi-pass transmembrane proteins that function as proton channels (Saotome et al, 2019). In vertebrates, these proteins play an essential role in regulating the timing, size, and shape of the developing otoconia, extracellular calcium carbonate biominerals that are required for vestibular functions (Hughes et al, 2004;Sollner et al, 2004;Kim et al, 2010).…”