Melki R, Cowan N J
Laboratoire d'Enzymologie, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
Mol Cell Biol. 1994 May;14(5):2895-904. doi: 10.1128/mcb.14.5.2895-2904.1994.
In the cytoplasm of eukaryotes, the folding of actins and tubulins is facilitated via interaction with a heteromeric toroidal complex (cytoplasmic chaperonin). The folding reaction consists of the formation of a binary complex between the unfolded target protein and the chaperonin, followed by the ultimate release of the native polypeptide in an ATP-dependent reaction. Here we show that the mitochondrial chaperonin (cpn60) and the cytoplasmic chaperonin both recognize a range of target proteins with different relative affinities; however, the cytoplasmic chaperonin shows the highest affinity for intermediates derived from unfolded tubulins and actins. These high-affinity actin and tubulin folding intermediates are distinct from the "molten globule" intermediates formed by noncytoskeletal target proteins in that they form relatively slowly. We show that the interaction between cytoplasmic chaperonin and unfolded target proteins depends on the chaperonin being in its ADP-bound state and that the release of the target protein occurs after a transition of the chaperonin to the ATP-bound state. Our data suggest a model in which ATP hydrolysis acts as a switch between conformational forms of the cytoplasmic chaperonin that interact either strongly or weakly with unfolded substrates.
在真核生物的细胞质中，肌动蛋白和微管蛋白通过与一种异源环形复合物（细胞质伴侣蛋白）相互作用来促进折叠。折叠反应包括未折叠的靶蛋白与伴侣蛋白之间形成二元复合物，随后在依赖ATP的反应中最终释放天然多肽。我们在此表明，线粒体伴侣蛋白（cpn60）和细胞质伴侣蛋白都能识别一系列具有不同相对亲和力的靶蛋白；然而，细胞质伴侣蛋白对源自未折叠微管蛋白和肌动蛋白的中间体具有最高亲和力。这些高亲和力的肌动蛋白和微管蛋白折叠中间体不同于非细胞骨架靶蛋白形成的“熔球态”中间体，因为它们形成得相对较慢。我们表明，细胞质伴侣蛋白与未折叠靶蛋白之间的相互作用取决于伴侣蛋白处于其结合ADP的状态，并且靶蛋白的释放发生在伴侣蛋白转变为结合ATP的状态之后。我们的数据提出了一个模型，其中ATP水解充当细胞质伴侣蛋白构象形式之间的开关，这些构象形式与未折叠底物的相互作用要么强要么弱。
