The structure of the carboxyl terminus of striated α-tropomyosin in solution reveals an unusual parallel arrangement of interacting α-helices
The structure of the carboxyl terminus of striated α-tropomyosin in solution reveals an unusual parallel arrangement of interacting α-helices
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DOI：
10.1021/bi026989e
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发表时间：
2003-01-28
期刊：
影响因子：
2.9
通讯作者：
Hitchcock-DeGregori, SE
中科院分区：
文献类型：
--
作者：
Greenfield, NJ;Swapna, GVT;Hitchcock-DeGregori, SE
盘状螺旋是众所周知的寡聚结构域，但它们也是蛋白质相互作用的重要部位。我们测定了含有横纹肌α-原肌球蛋白34个C-末端残基的二硫键、双链、37个残基的多肽TM9a(251-284)的核磁共振溶液结构和主干N-15松弛速率。TM9a(251-284)的核磁共振溶液结构与相关多肽的X射线结构的比较[Li，Y.，Mui，S.，Brown，J.H.Strand，J.，Reshetnikova，L.，Tobacman，L.S.，and Cohen，C.(2002)Proc.娜塔莉。阿卡德。SCI。U.S.A.99,7378-7383]揭示了显著的差异。在溶液中，残基253-269(像大多数原肌球蛋白分子一样)形成一个典型的盘绕线圈。然而，270-279残基是平行的、线性的螺旋，是原肌球蛋白的新发现。平行螺旋之间的堆积是由不寻常的界面残基造成的，这种残基对于盘绕线圈来说是非典型的。Y267在盘绕-盘绕界面的堆积较差，R-2驰豫速率低于邻近残基，表明该残基周围存在构象柔性。最后五个残基是非螺旋的和柔性的。平行螺旋的外露表面以及Y267和末端周围的弹性，可能有助于与肌钙蛋白T结合，并与原肌球蛋白和肌动蛋白的N-端形成复合体。我们认为，异常的堆积和灵活性是蛋白质中参与分子间相互作用的螺旋卷曲结构域的一般特征。
Coiled coils are well-known as oligomerization domains, but they are also important sites of protein-protein interactions. We determined the NMR solution structure and backbone N-15 relaxation rates of a disulfide cross-linked, two-chain, 37-residue polypeptide containing the 34 C-terminal residues of striated muscle a-tropomyosin, TM9a(251-284). The peptide binds to the N-terminal region of TM and to the tropomyosin-binding domain of the regulatory protein, troponin T. Comparison of the NMR solution structure of TM9a(251-284) with the X-ray structure of a related peptide [Li, Y., Mui, S., Brown, J. H., Strand, J., Reshetnikova, L., Tobacman, L. S., and Cohen, C. (2002) Proc. Natl. Acad. Sci. U.S.A. 99, 7378-7383] reveals significant differences. In solution, residues 253-269 (like most of the tropomyosin molecule) form a canonical coiled coil. Residues 270-279, however, are parallel, linear helices, novel for tropomyosin. The packing between the parallel helices results from unusual interface residues that are atypical for coiled coils. Y267 has poor packing at the coiled-coil interface and a lower R-2 relaxation rate than neighboring residues, suggesting there is conformational flexibility around this residue. The last five residues are nonhelical and flexible. The exposed surface presented by the parallel helices, and the flexibility around Y267 and the ends, may facilitate binding to troponin T and formation of complexes with the N-terminus of tropomyosin and actin. We propose that unusual packing and flexibility are general features of coiled-coil domains in proteins that are involved in intermolecular interactions.