Whitby F G, Phillips G N
Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005, USA.
Proteins. 2000 Jan 1;38(1):49-59.
Tropomyosin is a 400A-long coiled coil that polymerizes to form a continuous filament that associates with actin in muscle and numerous non-muscle cells. Tropomyosin and troponin together form a calcium-sensitive switch that is responsible for thin-filament regulation of striated muscle. Subtle structural features of the molecule, including non-canonical aspects of its coiled-coil motif, undoubtedly influence its association with f-actin and its role in thin filament regulation. Previously, careful inspection of native diffraction intensities was sufficient to construct a model of tropomyosin at 9A resolution in a spermine-induced crystal form that diffracts anisotropically to 4A resolution. Single isomorphous replacement (SIR) phasing has now provided an empirical determination of the structure at 7A resolution. A novel method of heavy-atom analysis was used to overcome difficulties in interpretation of extremely anisotropic diffraction. The packing arrangement of the molecules in the crystal, and important aspects of the tropomyosin geometry such as non-uniformities of the pitch and variable bending and radius of the coiled coil are evident.
原肌球蛋白是一种长400埃的卷曲螺旋，它聚合形成一条连续的细丝，在肌肉和许多非肌肉细胞中与肌动蛋白结合。原肌球蛋白和肌钙蛋白共同形成一个钙敏感开关，负责横纹肌细肌丝的调节。该分子的细微结构特征，包括其卷曲螺旋基序的非典型方面，无疑会影响其与丝状肌动蛋白的结合及其在细肌丝调节中的作用。此前，仔细检查天然衍射强度足以构建出精胺诱导晶体形式下9埃分辨率的原肌球蛋白模型，该晶体的各向异性衍射分辨率可达4埃。单对同晶置换（SIR）法现已给出了7埃分辨率下该结构的经验性测定结果。一种新的重原子分析方法被用于克服解释极各向异性衍射时的困难。晶体中分子的堆积排列以及原肌球蛋白几何结构的重要方面，如螺距的不均匀性以及卷曲螺旋的可变弯曲和半径，都很明显。
