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Three-dimensional structure of the myosin V inhibited state by cryoelectron tomography

机译：低温电子层析成像对肌球蛋白V抑制状态的三维结构

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Unconventional myosin V (myoV) is an actin-based molecular motor that has a key function in organelle and mRNA transport, as well as in membrane trafficking(1). MyoV was the first member of the myosin superfamily shown to be processive, meaning that a single motor protein can 'walk' hand-over-hand along an actin filament for many steps before detaching(2-4). Full-length myoV has a low actin-activated MgATPase activity at low [Ca2+], whereas expressed constructs lacking the cargo-binding domain have a high activity regardless of [Ca2+] (refs 5 - 7). Hydrodynamic data and electron micrographs indicate that the active state is extended, whereas the inactive state is compact(8-10). Here we show the first three-dimensional structure of the myoV inactive state. Each myoV molecule consists of two heads that contain an amino-terminal motor domain followed by a lever arm that binds six calmodulins. The heads are followed by a coiled-coil dimerization domain (S2) and a carboxy-terminal globular cargo-binding domain. In the inactive structure, bending of myoV at the head S2 junction places the cargo-binding domain near the motor domain's ATP-binding pocket, indicating that ATPase inhibition might occur through decreased rates of nucleotide exchange. The actin-binding interfaces are unobstructed, and the lever arm is oriented in a position typical of strong actin-binding states. This structure indicates that motor recycling after cargo delivery might occur through transport on actively treadmilling actin filaments rather than by diffusion.
机译：非常规肌球蛋白V（myoV）是一种基于肌动蛋白的分子马达，在细胞器和mRNA的运输以及膜运输中起关键作用（1）。 MyoV是肌球蛋白超家族的第一个成员，显示其是进行性的，这意味着单个运动蛋白可以在分离前沿着肌动蛋白丝“行走”许多步骤（2-4）。全长的myoV在低[Ca2 +]时具有较低的肌动蛋白激活MgATPase活性，而缺乏货物结合域的表达构建体则具有高活性，而与[Ca2 +]无关（参考文献5-7）。流体力学数据和电子显微照片表明，活性状态扩展，而非活性状态紧凑（8-10）。在这里，我们显示了myoV非活动状态的第一个三维结构。每个myoV分子由两个头部组成，两个头部包含一个氨基末端运动结构域，后跟一个与六个钙调蛋白结合的杠杆臂。头部后面是卷曲螺旋二聚结构域（S2）和羧基末端球状货物结合结构域。在非活性结构中，头部S2连接处的myoV弯曲将货物结合结构域置于运动结构域的ATP结合口袋附近，表明ATPase抑制可能通过核苷酸交换速率降低而发生。肌动蛋白结合界面畅通无阻，杠杆臂处于强肌动蛋白结合状态的典型位置。这种结构表明，货物交付后的马达回收可能是通过在主动跑步机上的肌动蛋白丝上运输而不是通过扩散进行的。

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