Kusunoki Hideki, Minasov George, Macdonald Ruby I, Mondragón Alfonso
Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, 2205 Tech Drive, Evanston, IL 60208, USA.
J Mol Biol. 2004 Nov 19;344(2):495-511. doi: 10.1016/j.jmb.2004.09.019.
Previous X-ray crystal structures have shown that linkers of five amino acid residues connecting pairs of chicken brain alpha-spectrin and human erythroid beta-spectrin repeats can undergo bending without losing their alpha-helical structure. To test whether bending at one linker can influence bending at an adjacent linker, the structures of two and three repeat fragments of chicken brain alpha-spectrin have been determined by X-ray crystallography. The structure of the three-repeat fragment clearly shows that bending at one linker can occur independently of bending at an adjacent linker. This observation increases the possible trajectories of modeled chains of spectrin repeats. Furthermore, the three-repeat molecule crystallized as an antiparallel dimer with a significantly smaller buried interfacial area than that of alpha-actinin, a spectrin-related molecule, but large enough and of a type indicating biological specificity. Comparison of the structures of the spectrin and alpha-actinin dimers supports weak association of the former, which could not be detected by analytical ultracentrifugation, versus strong association of the latter, which has been observed by others. To correlate features of the structure with solution properties and to test a previous model of stable spectrin and dystrophin repeats, the number of inter-helical interactions in each repeat of several spectrin structures were counted and compared to their thermal stabilities. Inter-helical interactions, but not all interactions, increased in parallel with measured thermal stabilities of each repeat and in agreement with the thermal stabilities of two and three repeats and also partial repeats of spectrin.
先前的X射线晶体结构表明，连接鸡脑α-血影蛋白和人红细胞β-血影蛋白重复序列对的五个氨基酸残基的连接子可以发生弯曲而不失去其α-螺旋结构。为了测试一个连接子的弯曲是否会影响相邻连接子的弯曲，通过X射线晶体学确定了鸡脑α-血影蛋白的两个和三个重复片段的结构。三个重复片段的结构清楚地表明，一个连接子的弯曲可以独立于相邻连接子的弯曲而发生。这一观察结果增加了血影蛋白重复序列模型链的可能轨迹。此外，三个重复分子结晶为反平行二聚体，其埋藏界面面积明显小于血影蛋白相关分子α-辅肌动蛋白，但足够大且属于表明生物学特异性的类型。血影蛋白和α-辅肌动蛋白二聚体结构的比较支持了前者的弱结合（这无法通过分析超速离心检测到），而后者的强结合已被其他人观察到。为了将结构特征与溶液性质相关联，并测试先前关于稳定血影蛋白和肌营养不良蛋白重复序列的模型，对几种血影蛋白结构的每个重复中的螺旋间相互作用数量进行了计数，并与它们的热稳定性进行了比较。螺旋间相互作用（但不是所有相互作用）与每个重复的测量热稳定性平行增加，并且与血影蛋白的两个和三个重复以及部分重复的热稳定性一致。
