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. Author manuscript; available in PMC: 2019 Dec 4.
Published in final edited form as: Nat Struct Mol Biol. 2019 Jun 3;26(6):518–525. doi: 10.1038/s41594-019-0235-9

Figure 1. Proton channel function and structures of Otop1 and Otop3 homodimers in lipid nanodiscs.

Figure 1.

a, currents measured by whole-cell patch clamp recording in HEK-293 cells expressing zfOtop1 (top) or chOtop3 (bottom) in response to acidic extracellular solutions with the indicated pH (pHi = 7.4, Vm = −80 mV). Inset of top panel shows inhibition of zfOtop1 currents by 1 mM Zn2+ (pink bar). b, orthogonal views of sharpened cryo-EM maps of zfOtop1. One subunit is colored dark and light shades of purple, while the other subunit is colored green and light green. Each subunit has a structurally homologous N domain (dark shade) and C domain (light shade). The center of the dimer contains a tunnel occupied by cholesterol-like densities. Putative cholesterol and lipid densities are colored light orange. c, orthogonal views of sharpened cryo-EM maps of chOtop3, colored as in b. d, side (left) and top (right) views of model of Otop1 dimer showing TM helices as cylinders. One subunit is colored gray while in the other subunit each of the twelve TM helices are colored differently and numbered. In the right panel, the central two-fold symmetry axis is depicted as a black oval, and pseudosymmetry axes relating the N domain and C domain within each subunit are depicted as empty red ovals. e, schematic of Otop1 structure, with TM helices colored corresponding to c. Loops not modeled due to poor density are depicted as dashed gray lines. f, structural alignment of the N domain (red) and C domain (blue).