Molecular Basis of Transduction in Auditory Sensory Organs

1)顶杆结构：在浇注弹簧模型中 换能器，力通过增加施加在换能器通道上 蛋白质细丝(尖端连接)中跨越距离的张力 在两个相邻的立体纤毛之间。使用冷冻蚀刻电子 显微镜(EM)我们观察到尖端的链节是由一个8 至11 nm右手缠绕(间距为60 nm)双丝 它以多个插入点结束，位于 立体纤毛。这表明可能存在多个通道 每个尖端链接并联工作，也串联中频传感器 通道确实存在于链路的两端。卷曲蛋白 众所周知，细丝特别稳定，因为它们的内部 结构可以平衡压缩和拉伸。肌动蛋白细丝，用于 例如，具有非常高的弯曲和扭转刚度。给定 顶杆的长度较短，结构上与 肌动蛋白细丝，我们假设顶端-连接也可能有一个非常 高弯曲和扭转刚度。这样的属性很可能是 控制传感器通道选通的基本原理 特别是在声频的动态条件下。2) 细胞外膜机制的分子组织 毛细胞(OHC)电动。我们之前已经表明， 电动依赖于一种结合在 侧质膜的结构。使用冷冻蚀刻EM 我们观察到侧质膜的表面 OHC的表面覆盖着由致密堆积组成的斑块 蛋白质颗粒。对这些斑块的图像处理显示 高度组织的粒子正交数组，具有 中心到中心的距离为13 nm。邻近的斑块显示 这些蛋白质晶格的取向角度略有不同。这个 斑块的马赛克或瓷砖组织似乎与我们的 先前的观察表明，潜在的皮质细胞骨架有一个 格子组织。蛋白质颗粒的外质结构域 在电池的外表面上是浅的，并且看起来不 喝一杯甘露糖。每个颗粒的细胞质结构域出现 比外质体大，呈球状。此外 对于垂直堆积的颗粒，侧向质膜 包含与柱状图案相匹配的颗粒的线性阵列 将质膜物理地耦合到 潜在的皮质细胞骨架。正交系斑块 包装的蛋白质很可能对应于 电动机制。电压驱动的构象变化 这些蛋白质阵列会产生区域变化，从而推动 外毛细胞电动势。

1) Tip link structure: In the gating-spring model of transduction, forces are applied to transducer channels by increased tension in a protein filament (the tip link) that spans the distance between two adjacent stereocilia. Using freeze- etching electron microscopy (EM) we have observed that the tip link is made of an 8 to 11 nm right-handed coiled (with a 60 nm pitch) double-filament that ends in multiple insertion points on the membrane of the stereocilia. This indicates that there may be more than one channel per tip-link working in parallel, and also in series if transducer channels are indeed present at either end of the link. Coiled protein filaments are known to be particularly stable because their internal structure can balance compression and tension. Actin filaments, for example, have a very high flexural and torsional rigidity. Given the short length of the tip-link and the similarity in structure with the actin filament, we postulate that the tip-link may also have a very high flexural and torsional rigidity. Such properties are likely to be fundamental in the control of the gating of the transducer channel especially under dynamic conditions at acoustic frequencies. 2) Molecular organization of the membrane-based mechanism of outer hair cell (OHC) electromotility. We have previously shown that electromotility depends on a mechanism incorporated in the structure of the lateral plasma membrane. Using freeze-etching EM we have observed that the surface of the lateral plasma membrane of the OHC is covered with plaques consisting of a dense packing of protein particles. Image processing of these plaques revealed a highly organized orthogonal array of particles with a center-to-center distance of 13nm. Neighboring plaques show slightly different angles of orientation of these protein lattices. The mosaic or tile organization of the plaques appears to match our previous observation that the underlying cortical cytoskeleton has a lattice organization. The exoplasmic domain of the protein particles on the external surface of the cell is shallow and does not appear to have a glycocalyx. The cytoplasmic domain of each particle appears larger than the exoplasmic one and has a globular shape. In addition to the orthogonally packed particles, the lateral plasma membrane contains linear arrays of particles that match the pattern of pillar structures that physically couple the plasma membrane to the underlying cortical cytoskeleton. The plaques of orthogonally packed proteins likely correspond to units of organization of the electromotility mechanism. Voltage driven conformation changes in these arrays of proteins would produce the area changes that drive outer hair cell electromotility.