The structural stability of the co-chaperonin GroES
The structural stability of the co-chaperonin GroES
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DOI：
10.1006/jmbi.1997.1263
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发表时间：
1997-10-10
影响因子：
5.6
通讯作者：
Freire, E
中科院分区：
文献类型：
--
作者：
Boudker, O;Todd, MJ;Freire, E
采用高灵敏度差示扫描量热法和圆二色法研究了共伴侣蛋白GroES在不同溶剂条件下的结构稳定性。GroES的热折叠/展开是一个自发的可逆过程，涉及折叠七聚体和未折叠单体之间的高度合作转变。在变性过程中，折叠单体在能量上是不利的，因此永远不会被填充到一个可观的程度。对高分辨率结构的分析表明，与具有相似分子质量的典型球状蛋白相比，GroES分离的折叠单体所覆盖的总表面比例要小得多。由于这个原因，每个GroES单体的分子内相互作用似乎不足以实现热力学稳定。七聚体结构的稳定主要是由于亚基间的相互作用而不是亚基内的相互作用。这些相互作用在焓和熵上都有利于寡聚化。尽管带电残基密度很高，但在PH为7时，GroES的稳定性对盐浓度没有明显的依赖性。另一方面，毫摩尔浓度的镁可能通过特异性结合使GroES稳定下来。Mg2+引起的稳定与每七聚体约有3个结合位点的解离常数为0.5 mM相一致，这些结果强调了四级结构在小寡聚蛋白稳定中的作用。(C) 1997学术出版社有限公司
The structural stability of the co-chaperonin GroES has been studied by high sensitivity differential scanning calorimetry and circular dichroism under different solvent conditions. The thermal folding/unfolding of GroES is a spontaneous reversible process involving a highly cooperative transition between folded heptamers and unfolded monomers. During the-denaturation process folded monomers are energetically unfavorable and consequently never become populated to an appreciable degree. Analysis of the high resolution structure indicates that isolated folded monomers of GroES bury a significantly smaller fraction of their total surface than typical globular proteins of similar molecular mass. For this reason the intramolecular interactions within each GroES monomer appear not to be sufficient for thermodynamic stabilization. The stabilization of the heptameric structure is due primarily to intersubunit interactions rather than intrasubunit interactions. These interactions favor oligomerization both enthalpically and entropically. Despite the high density of charged residues, the stability of GroES shows no measurable dependence on salt concentration at PH 7. On the other hand, millimolar concentrations of magnesium stabilize GroES, presumably by specific binding. The stabilization elicited by Mg2+ is consistent with a dissociation constant of the order of 0.5 mM and approximately three binding sites per heptamer, These results emphasize the role of quaternary structure in the stabilization of small oligomeric proteins. (C) 1997 Academic Press Limited.