1.A.110.1.2
OTOP1 H⁺ channel of 612 aas and 10 TMSs in an apparent 4 + 4 + 2 TMS arrangement (Tu et al. 2018). OTOP1 is a protein required for development of gravity-sensing otoconia in the vestibular system. It forms a proton-selective ion channel (Tu et al. 2018). Proton channel activity is only weakly-sensitive to voltage and is probably required in cell types that use changes in intracellular pH for cell signaling or to regulate biochemical or developmental processes (Tu et al. 2018). In the vestibular system of the inner ear, it is required for the formation and function of otoconia, calcium carbonate crystals that sense gravity and acceleration. It regulates purinergic control of intracellular calcium in vestibular supporting cells and may be involved in sour taste perception in sour taste cells by mediating entry of protons within the cytosol. It is also involved in energy metabolism, by reducing adipose tissue inflammation and protecting from obesity-induced metabolic dysfunction. Two extracellular loops in the human Otop1 proton channel function in proton sensing and transport (Li et al. 2022).