Abstract：
The M-line of striated muscle is a complex structure that anchors myosin-containing thick filaments and also participates in signaling and proteostasis. While the physical associations among many M-line components have been defined, the mechanism of thick filament attachment is not completely understood. In Caenorhabditis elegans, myosin A is essential for viability and forms the site of M-line attachment at the center of the filament, whereas myosin B forms the filament arms. Using a mutant myosin A that forms ectopic filaments, we examined interactions between myosin A and M-line proteins in intact muscle cells. Ectopic myosin A recruits the giant kinase UNC-89/obscurin, a presumed scaffolding protein, in an interaction that requires the zinc-finger protein UNC-98, but not UNC-82/NUAK, UNC-97/PINCH, or UNC-96. In myosin A mutants, UNC-89/obscurin patterning is highly defective in embryos and adults. A chimeric myosin containing 169 residues of the myosin A C-terminal rod, coincident with the UNC-98/ZnF binding site, is sufficient for colocalization of UNC-89/obscurin and UNC-98/ZnF in M-line structures whereas a myosin chimera lacking these residues colocalizes with UNC-89/obscurin in M-lines that lack UNC-98. Thus, at least two myosin A rod regions contribute independently to M-line organization. We hypothesize that these M-line-organizing functions correspond to the essential \"filament initiation function\" performed by this isoform.
摘要：
横纹肌的M线是锚定含肌球蛋白的粗丝并且还参与信号传导和蛋白抑制的复杂结构。虽然已经定义了许多M线组件之间的物理关联，粗丝附着的机制还没有完全理解。在秀丽隐杆线虫中,肌球蛋白A对生存能力至关重要，并在细丝中心形成M线附着位点，而肌球蛋白B形成细丝臂。使用形成异位细丝的突变肌球蛋白A，我们研究了完整肌细胞中肌球蛋白A和M-line蛋白之间的相互作用。异位肌球蛋白A招募了巨大的激酶UNC-89/obscurin，一种假定的支架蛋白，在需要锌指蛋白UNC-98而不是UNC-82/NUAK的相互作用中，UNC-97/PINCH,或者UNC-96.在肌球蛋白A突变体中，UNC-89/obscurin模式在胚胎和成虫中是高度缺陷的。一种嵌合肌球蛋白，含有肌球蛋白AC末端棒的169个残基，与UNC-98/ZnF结合位点一致，对于M-系结构中UNC-89/obscurin和UNC-98/ZnF的共定位是足够的,而缺乏这些残基的肌球蛋白嵌合体与缺乏UNC-98的M-系中的UNC-89/obscurin共定位。因此，至少两个肌球蛋白A杆区独立地贡献M线组织。我们假设这些M线组织功能对应于该同工型执行的基本“细丝启动功能”。
