Thermal Stabilities of brain spectrin and the constituent repeats of subunits
Thermal Stabilities of brain spectrin and the constituent repeats of subunits
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DOI：
10.1021/bi061368x
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发表时间：
2006-11-14
期刊：
影响因子：
2.9
通讯作者：
Mohandas, Narla
中科院分区：
文献类型：
--
作者：
An, Xiuli;Zhang, Xihui;Mohandas, Narla
编码哺乳动物血影蛋白的不同基因产生在其表观硬度方面不同的蛋白质。为了探索这一点，我们比较了热稳定性的脑血影蛋白亚基（α II和β II）与红细胞血影蛋白（RI和，我）的结构重复。36个α II-和β II-血影蛋白重复序列的解折叠转变中点（T-m）在24和82 ℃之间延伸，平均比α I-和β I-血影蛋白重复序列高约10 ℃。这种差异反映在完整脑和红细胞血影蛋白的T-m值中。来自脑血影蛋白的三个串联重复结构中的两个表现出强的协同偶联，较不稳定的配偶体的Tm升高对应于约-4.4和-3.5千卡/摩尔的偶联自由能。相比之下，第三个串联重复结构表现出可忽略的协同性。串联重复突变体，其中连接两个结构域的“接头”螺旋的一部分被来自红细胞血影蛋白的相应螺旋片段取代，仅显示出微小的热熔融曲线扰动，而没有协同性的破坏。因此，接头区，容忍很少的点突变而不丧失合作功能，显然已经发展到允许特定区域的构象偶联。α II-和β II-血影蛋白中重复序列的更大结构稳定性可以至少部分地解释与红细胞血影蛋白相比脑的更高刚性。
The different genes that encode mammalian spectrins give rise to proteins differing in their apparent stiffness. To explore this, we have compared the thermal stabilities of the structural repeats of brain spectrin subunits (alpha II and beta II) with those of erythrocyte spectrin ( RI and, I). The unfolding transition midpoints (T-m) of the 36 alpha II- and, beta II- spectrin repeats extend between 24 and 82 degrees C, with an average higher by some 10 degrees C than that of the alpha I- and, beta I- spectrin repeats. This difference is reflected in the T-m values of the intact brain and erythrocyte spectrins. Two of three tandem-repeat constructs from brain spectrin exhibited strong cooperative coupling, with elevation of the T-m of the less stable partner corresponding to coupling free energies of approximately -4.4 and -3.5 kcal/mol. The third tandem-repeat construct, by contrast, exhibited negligible cooperativity. Tandem- repeat mutants, in which a part of the "linker" helix that connects the two domains was replaced with a corresponding helical segment from erythroid spectrin, showed only minor perturbation of the thermal melting profiles, without breakdown of cooperativity. Thus, the linker regions, which tolerate few point mutations without loss of cooperative function, have evidently evolved to permit conformational coupling in specified regions. The greater structural stability of the repeats in alpha II- and, beta II- spectrin may account, at least in part, for the higher rigidity of brain compared to erythrocyte spectrin.