Two-crystal structures of tropomyosin C-terminal fragment 176-273: exposure of the hydrophobic core to the solvent destabilizes the tropomyosin molecule.
Two-crystal structures of tropomyosin C-terminal fragment 176-273: exposure of the hydrophobic core to the solvent destabilizes the tropomyosin molecule.
复制标题
DOI：
10.1529/biophysj.107.126144
复制
发表时间：
2008-07
影响因子：
3.4
通讯作者：
S. Minakata;K. Maéda;N. Oda;K. Wakabayashi;Y. Nitanai;Y. Maéda
中科院分区：
文献类型：
--
作者：
S. Minakata;K. Maéda;N. Oda;K. Wakabayashi;Y. Nitanai;Y. Maéda
原肌球蛋白（Tropomyosin，Tm）是一种双链α-螺旋卷曲螺旋蛋白，当与肌钙蛋白结合时，它负责脊椎动物骨骼肌和心肌中基于肌动蛋白的肌肉收缩调节。目前普遍认为Tm是一种柔性的棒状结构，柔性在其功能中起着至关重要的作用。为了获得更多关于Tm的灵活性的信息，我们求解并比较了相同C-末端片段的两个晶体结构，跨越整个长度的约40%。我们还比较了这些结构与我们以前报道的晶体结构的一个几乎相同的Tm段在一个不同的晶体形式。指定局部卷曲螺旋几何形状的参数，例如两个螺旋之间的间隔和局部螺距，以与三种晶体结构中相同的方式沿Tm的长度沿着波动，表明这些参数由氨基酸序列定义。在分离增加的区域中，在Glu-218和Gln-263周围，疏水核心被三个孔破坏。此外，据我们所知，对于Tm，在这些孔中首次发现了水分子。在某些结构中，空穴周围的B因子高于分子的其余部分。Tm卷曲螺旋必须是不稳定的，因此不仅在丙氨酸簇中而且在断裂核心的区域中可能是柔性的。仔细观察两条链之间的局部交错和局部弯曲揭示了应变在丙氨酸簇处积累，并且可以在断裂的核心区域中松弛。此外，即使在有限数量的点处可能发生类似弯曲的变形时，应变也分布在长范围内。因此，Tm不应被视为由柔性接头连接的一系列短刚性杆，而应被视为用相对更柔性的区域修补的无缝橡胶杆。
Tropomyosin (Tm) is a two-stranded alpha-helical coiled-coil protein, and when associated with troponin, it is responsible for the actin filament-based regulation of muscle contraction in vertebrate skeletal and cardiac muscles. It is widely believed that Tm adopts a flexible rod-like structure in which the flexibility must play a crucial role in its functions. To obtain more information about the flexibility of Tm, we solved and compared two crystal structures of the identical C-terminal segments, spanning approximately 40% of the entire length. We also compared these structures with our previously reported crystal structure of an almost identical Tm segment in a distinct crystal form. The parameters specifying the local coiled-coil geometry, such as the separation between two helices and the local helical pitch, undulate along the length of Tm in the same way as among the three crystal structures, indicating that these parameters are defined by the amino acid sequence. In the region of increased separation, around Glu-218 and Gln-263, the hydrophobic core is disrupted by three holes. Moreover, for the first time to our knowledge, for Tm, water molecules have been identified in these holes. In some structures, the B-factors are higher around the holes than in the rest of the molecule. The Tm coiled-coil must be destabilized and therefore may be flexible, not only in the alanine clusters but also in the regions of the broken core. A closer look at the local staggering between the two chains and the local bending revealed that the strain accumulates at the alanine cluster and may be relaxed in the broken core region. Moreover, the strain is distributed over a long range, even when a deformation like bending may occur at a limited number of spots. Thus, Tm should not be regarded as a train of short rigid rods connected by flexible linkers, but rather as a seamless rubber rod patched with relatively more flexible regions.