Jontes J D, Wilson-Kubalek E M, Milligan R A
Department of Cell Biology, Scripps Research Institute, La Jolla, California 92037, USA.
Nature. 1995 Dec 14;378(6558):751-3. doi: 10.1038/378751a0.
Brush border myosin I (BBMI) is a single-headed, unconventional myosin from intestinal microvilli, composed of a heavy chain of relative molecular mass 119,000 (M(r) 119K) and three calmodulin light chains. Although believed to have a largely structural role, it exhibits the normal actin-activated ATPase and motility properties of a member of the myosin superfamily. Here we present three-dimensional maps of BBMI-decorated actin filaments with and without bound MgADP. While the motor domain remains in a state similar to rigor, the light-chain-binding domain swings through approximately 32 degrees, resulting in a approximately 50-A movement at the end of the region visualized (the second calmodulin light chain). This could correspond to approximately 72-A movement of the entire domain. Although qualitatively similar to the movement observed in myosin II, the magnitude of the change is sufficiently different to suggest that structural changes during the actomyosin ATPase cycle differ among myosins, possibly reflecting adaptation for specialized functional demands.
刷状缘肌球蛋白I（BBMI）是一种来自肠道微绒毛的单头非传统肌球蛋白，由一条相对分子质量为119,000（M(r) 119K）的重链和三条钙调蛋白轻链组成。尽管人们认为它主要起结构作用，但它具有肌球蛋白超家族成员正常的肌动蛋白激活ATP酶活性和运动特性。在这里，我们展示了结合和未结合MgADP的BBMI修饰的肌动蛋白丝的三维图谱。虽然运动结构域保持类似于僵直的状态，但轻链结合结构域摆动约32度，导致在可视化区域末端（第二条钙调蛋白轻链）产生约50埃的移动。这可能对应于整个结构域约72埃的移动。尽管在性质上与在肌球蛋白II中观察到的移动相似，但变化的幅度差异足够大，表明在肌动球蛋白ATP酶循环期间不同肌球蛋白的结构变化不同，这可能反映了对特殊功能需求的适应。
