Farr G W, Scharl E C, Schumacher R J, Sondek S, Horwich A L
Department of Genetics and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Cell. 1997 Jun 13;89(6):927-37. doi: 10.1016/s0092-8674(00)80278-0.
The eukaryotic cytosolic chaperonin, CCT, plays an essential role in mediating ATP-dependent folding of actin and tubulin. There is debate about whether it mediates folding through a single round of association followed by release of native forms, or through cycles of binding and full release in which only a fraction of released molecules reaches native form in any cycle. We examine the fate of newly synthesized substrate proteins bound to CCT in reticulocyte lysate or intact Xenopus oocytes. When a chaperonin "trap," able to bind but not release substrate protein, is introduced, production of the native state is strongly inhibited, associated with transfer to trap. While predominantly nonnative forms of actin, tubulin, and a newly identified substrate, G(alpha)-transducin, are released from CCT, a small fraction reaches native form with each round of release, inaccessible to trap. This overall mechanism resembles that of the bacterial chaperonin, GroEL.
真核细胞胞质伴侣蛋白CCT在介导肌动蛋白和微管蛋白的ATP依赖性折叠过程中发挥着重要作用。关于它是通过一轮结合随后释放天然形式来介导折叠，还是通过结合和完全释放的循环来介导折叠（在任何一个循环中只有一小部分释放的分子达到天然形式），目前存在争议。我们研究了在网织红细胞裂解物或完整非洲爪蟾卵母细胞中与CCT结合的新合成底物蛋白的命运。当引入一种能够结合但不能释放底物蛋白的伴侣蛋白“陷阱”时，天然状态的产生会受到强烈抑制，并与转移到陷阱中相关联。虽然肌动蛋白、微管蛋白以及一种新鉴定的底物Gα转导蛋白主要以非天然形式从CCT中释放出来，但每一轮释放都有一小部分达到天然形式，不受陷阱影响。这种整体机制类似于细菌伴侣蛋白GroEL的机制。
