Department of Physiology, University of Texas Southwestern Medical Center, Dallas, United States.
Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, United States.
Elife. 2019 Apr 11;8:e46710. doi: 10.7554/eLife.46710.
The otopetrin (OTOP) proteins were recently characterized as proton channels. Here we present the cryo-EM structure of OTOP3 from (XtOTOP3) along with functional characterization of the channel. XtOTOP3 forms a homodimer with each subunit containing 12 transmembrane helices that can be divided into two structurally homologous halves; each half assembles as an α-helical barrel that could potentially serve as a proton conduction pore. Both pores open from the extracellular half before becoming occluded at a central constriction point consisting of three highly conserved residues - Gln-Asp/Asn-Tyr (the constriction triads). Mutagenesis shows that the constriction triad from the second pore is less amenable to perturbation than that of the first pore, suggesting an unequal contribution between the two pores to proton transport. We also identified several key residues at the interface between the two pores that are functionally important, particularly Asp509, which confers intracellular pH-dependent desensitization to OTOP channels.
耳石蛋白（OTOP）最近被鉴定为质子通道。在这里，我们展示了来自（XtOTOP3）的 XtOTOP3 的冷冻电镜结构以及对通道功能的表征。XtOTOP3 形成同源二聚体，每个亚基包含 12 个跨膜螺旋，可以分为两个结构同源的半部分；每个半部分组装成一个 α-螺旋桶，可能作为质子传导孔。两个孔都从细胞外半部分打开，然后在由三个高度保守的残基（Gln-Asp/Asn-Tyr，即紧缩三联体）组成的中央紧缩点处被阻塞。突变显示第二孔的紧缩三联体比第一孔的紧缩三联体更不易受干扰，这表明两个孔在质子转运中贡献不均等。我们还在两个孔之间的界面处鉴定了几个功能重要的关键残基，特别是 Asp509，它赋予 OTOP 通道对细胞内 pH 依赖性脱敏。
