Eukaryotic type II chaperonin CCT interacts with actin through specific subunits
Eukaryotic type II chaperonin CCT interacts with actin through specific subunits
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DOI：
10.1038/45294
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发表时间：
1999-12-09
期刊：
影响因子：
64.8
通讯作者：
Valpuesta, JM
中科院分区：
文献类型：
--
作者：
Llorca, O;McCormack, EA;Valpuesta, JM
伴侣蛋白帮助其他蛋白质折叠(1)。II型伴侣蛋白，如含有TCP-1的伴侣蛋白（CCT），存在于古细菌和真核细胞质中(2)。它们是由一到八种不同多肽组成的十六聚体或非十聚体低聚物。然而，像GroEL这样的I型伴侣蛋白是混杂的，有助于许多其他蛋白质的折叠(1)，只有少数蛋白质，主要是肌动蛋白和微管蛋白，被描述为CCT的天然底物，这种特异性可能与8个CCT亚基的分化有关(3)。在这里，我们通过冷冻电子显微镜和图像处理获得了CCT和α -肌动蛋白复合物的三维重建。这表明cr-actin与两个CCT亚基中的任何一个的顶端结构域相互作用。针对两种特异性CCT亚基的抗体对CCT-底物复合物进行免疫标记表明，肌动蛋白通过两种特异性和不同的相互作用与CCT结合：肌动蛋白的小结构域与CCT δ结合，而大结构域与CCT β或CCT ε结合（均位于δ的1,4位）。这些结果表明，肌动蛋白与CCT的结合具有亚基特异性和几何依赖性，因此真核CCT的底物识别机制可能与原核GroEL不同。
Chaperonins assist the folding of other proteins(1). Type II chaperonins, such as chaperonin containing TCP-1(CCT), are found in archaea and in the eukaryotic cytosol(2). They are hexadecameric or nonadecameric oligomers composed of one to eight different polypeptides. Whereas type I chaperonins like GroEL are promiscuous, assisting in the folding of many other proteins(1) only a small number of proteins, mainly actin and tubulin, have been described as natural substrates of CCT, This specificity may be related to the divergence of the eight CCT subunits(3). Here we have obtained a three-dimensional reconstruction of the complex between CCT and alpha-actin by cryo-electron microscopy and image processing. This shows that cr-actin interacts with the apical domains of either of two CCT subunits. Immunolabelling of CCT-substrate complexes with antibodies against two specific CCT subunits showed that actin binds to CCT using two specific and distinct interactions: the small domain of actin binds to CCT delta and the large domain to CCT beta or CCT epsilon (both in position 1,4 with respect to delta). These results indicate that the binding of actin to CCT is both subunit-specific and geometry-dependent, Thus, the substrate recognition mechanism of eukaryotic CCT may differ from that of prokaryotic GroEL.