Structural basis for tropomyosin overlap in thin (actin) filaments and the generation of a molecular swivel by troponin-T
Structural basis for tropomyosin overlap in thin (actin) filaments and the generation of a molecular swivel by troponin-T
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DOI：
10.1073/pnas.0801950105
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发表时间：
2008-05-20
影响因子：
11.1
通讯作者：
Wakabayashi, Takeyuki
中科院分区：
文献类型：
--
作者：
Murakami, Kenji;Stewart, Murray;Wakabayashi, Takeyuki
原肌球蛋白的头-尾聚合对于其肌动蛋白结合、在肌动蛋白丝组装中的功能以及肌动蛋白-肌球蛋白收缩的调节至关重要。在这里，我们描述了含有重叠的原肌球蛋白IN和C末端（TM-N和TM-C）的晶体的2.1埃分辨率结构，以及含有TM-N和TM-C以及肌钙蛋白-T（TnT）片段的晶体的2.9埃分辨率结构。在每个连接处，TM-N的N-末端螺旋是张开的，其中只有一个与TM-C包装在一起。在TM-C的C-末端区域，卷曲螺旋核心中的关键水破坏了局部2重对称性，并有助于在一个螺旋上产生扭结。在TnT片段的存在下，TM-C中的不对称性促进含有两个TM-C链和TM-N和TnT各自的一个链的4-heix束的形成。突变产生TM-C不对称性的残基导致肌钙蛋白对肌动蛋白原肌球蛋白细丝的亲和力显著降低。TnT的高度保守区域，其中大多数心肌病突变，是至关重要的相互作用与原肌球蛋白。三元复合物的结构也解释了为什么骨骼肌和心肌特异性C-末端区域需要结合TnT，以及为什么原肌球蛋白同源二聚体仅结合单个TnT。在肌动蛋白丝上，头-尾连接可以起到分子旋转的作用，以适应连续原肌球蛋白之间卷曲螺旋路径的不规则性，从而使每个原肌球蛋白与肌动蛋白螺旋等效地相互作用。
Head-to-tail polymerization of tropomyosin is crucial for its actin binding, function in actin filament assembly, and the regulation of actin-myosin contraction. Here, we describe the 2.1 angstrom resolution structure of crystals containing overlapping tropomyosin IN and C termini (TM-N and TM-C) and the 2.9 angstrom resolution structure of crystals containing TM-N and TM-C together with a fragment of troponin-T (TnT). At each junction, the N-terminal helices of TM-N were splayed, with only one of them packing against TM-C. In the C-terminal region of TM-C, a crucial water in the coiled-coil core broke the local 2-fold symmetry and helps generate a kink on one helix. In the presence of a TnT fragment, the asymmetry in TM-C facilitates formation of a 4-heiix bundle containing two TM-C chains and one chain each of TM-N and TnT. Mutating the residues that generate the asymmetry in TM-C caused a marked decrease in the affinity of troponin for actin-tropomyosin filaments. The highly conserved region of TnT, in which most cardiomyopathy mutations reside, is crucial for interacting with tropomyosin. The structure of the ternary complex also explains why the skeletal- and cardiac-muscle specific C-terminal region is required to bind TnT and why tropomyosin homodimers bind only a single TnT. On actin filaments, the head-to-tail junction can function as a molecular swivel to accommodate irregularities in the coiled-coil path between successive tropomyosins enabling each to interact equivalently with the actin helix.