Liang W, Warrick H M, Spudich J A
Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305-5307, USA.
J Cell Biol. 1999 Nov 29;147(5):1039-48. doi: 10.1083/jcb.147.5.1039.
Myosin II thick filament assembly in Dictyostelium is regulated by phosphorylation at three threonines in the tail region of the molecule. Converting these three threonines to aspartates (3 x Asp myosin II), which mimics the phosphorylated state, inhibits filament assembly in vitro, and 3 x Asp myosin II fails to rescue myosin II-null phenotypes. Here we report a suppressor screen of Dictyostelium myosin II-null cells containing 3 x Asp myosin II, which reveals a 21-kD region in the tail that is critical for the phosphorylation control. These data, combined with new structural evidence from electron microscopy and sequence analyses, provide evidence that thick filament assembly control involves the folding of myosin II into a bent monomer, which is unable to incorporate into thick filaments. The data are consistent with a structural model for the bent monomer in which two specific regions of the tail interact to form an antiparallel tetrameric coiled-coil structure.
盘基网柄菌中肌球蛋白II粗丝组装受分子尾部区域三个苏氨酸磷酸化的调控。将这三个苏氨酸转变为天冬氨酸(3×天冬氨酸肌球蛋白II),模拟磷酸化状态,在体外抑制丝组装,且3×天冬氨酸肌球蛋白II无法挽救肌球蛋白II缺失型表型。在此我们报道了对含有3×天冬氨酸肌球蛋白II的盘基网柄菌肌球蛋白II缺失细胞的抑制子筛选,其揭示了尾部一个对磷酸化控制至关重要的21-kD区域。这些数据,结合来自电子显微镜和序列分析的新结构证据,提供了粗丝组装控制涉及肌球蛋白II折叠成弯曲单体的证据,该弯曲单体无法并入粗丝。这些数据与弯曲单体的结构模型一致,在该模型中尾部的两个特定区域相互作用形成反平行四聚体卷曲螺旋结构。