Stewart M, King K L, Roberts T M
M.R.C. Laboratory of Molecular Biology, Cambridge, U.K.
J Mol Biol. 1994 Oct 14;243(1):60-71. doi: 10.1006/jmbi.1994.1630.
The amoeboid motility nematode sperm is mediated by cytoskeletal filaments composed of major sperm protein (MSP). We have used electron microscopy and image processing to show that MSP filaments are constructed from two subfilament strands which are themselves formed from a helical arrangement of subunits. The subfilaments are based on left-handed helices of pitch 9 nm that then coil along right-handed helical tracks of pitch 22.5 nm to form filaments. The subfilaments appear to be indistinguishable from the helices present in orthorhombic crystals of MSP. Because in filaments the subfilaments are themselves helical, not all subunits are able to participate in protein-protein interactions between different strands. One consequence of this interaction geometry is that the same molecular interactions that function to assemble subfilaments into filaments can also be used to assemble filaments into larger supramolecular assemblies such as the macrofibres formed in vitro and the fibre bundles found in vivo in sperm pseudopods. These results indicate the importance of filament bundling in addition to vectorial filament assembly in amoeboid cell motility.
变形虫样运动的线虫精子由主要精子蛋白（MSP）组成的细胞骨架丝介导。我们利用电子显微镜和图像处理技术表明，MSP丝由两条亚丝链构成，而这两条亚丝链本身又由亚基的螺旋排列形成。亚丝基于螺距为9纳米的左手螺旋，然后沿着螺距为22.5纳米的右手螺旋轨道盘绕形成丝。这些亚丝似乎与MSP正交晶体中存在的螺旋难以区分。因为在丝中，亚丝本身是螺旋状的，并非所有亚基都能参与不同链之间的蛋白质-蛋白质相互作用。这种相互作用几何结构的一个结果是，将亚丝组装成丝的相同分子相互作用也可用于将丝组装成更大的超分子聚集体，如体外形成的大纤维和精子伪足中体内发现的纤维束。这些结果表明，除了在变形虫样细胞运动中矢量丝组装外，丝束形成也很重要。
