Molecular Basis of Transduction in Auditory Sensory Organs

1)叶尖连杆结构： 换能，力通过增加的力施加到换能器通道。 蛋白质细丝（尖端连接）中的张力， 在两个相邻的静纤毛之间。利用冷冻蚀刻电子 我们已经观察到，尖端链接是由8 到11 nm的右手盘绕（具有60 nm间距）双灯丝 其终止于膜上的多个插入点， 静纤毛这表明可能存在不止一个通道 每个头端连杆并联工作，如果传感器串联工作， 信道实际上存在于链路的任一端。卷曲蛋白质 已知长丝是特别稳定的，因为它们的内部 结构可以平衡压缩和拉伸。肌动蛋白丝，用于 例如，具有非常高的弯曲和扭转刚度。鉴于 尖端连杆长度短，结构与 肌动蛋白丝，我们假设，尖端链接也可能有一个非常 高抗弯和抗扭刚度。这些财产很可能是 传感器通道选通控制的基础 特别是在声频的动态条件下。（二） 外膜机制的分子组织 毛细胞（OHC）电活动性。我们之前已经证明， 电动性依赖于一种机制， 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填料组成的斑块 蛋白质颗粒。对这些斑块的图像处理显示， 高度有序的正交颗粒阵列， 中心到中心的距离为13nm。附近的牌匾显示 这些蛋白质晶格的取向角度略有不同。的 镶嵌或瓷砖组织的牌匾似乎符合我们的 先前的观察表明，底层皮层细胞骨架具有 晶格组织蛋白质颗粒的胞外区 在细胞的外表面上是浅的，并且看起来不 有一个糖萼。每个颗粒的胞质结构域出现 比外质大，呈球形。此外 对于正交排列的颗粒， 含有与柱子图案相匹配的粒子线性阵列 将质膜物理耦合到膜的结构， 在皮层细胞骨架下面。正交的斑块 包装的蛋白质可能对应于组织的单位， 电运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， 外毛细胞电活动性。

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.