Tian G, Vainberg I E, Tap W D, Lewis S A, Cowan N J
Department of Biochemistry, New York University Medical Center, New York 10016, USA.
J Biol Chem. 1995 Oct 13;270(41):23910-3. doi: 10.1074/jbc.270.41.23910.
Chaperonins are known to facilitate protein folding, but their mechanism of action is not well understood. The fact that target proteins are released from and rebind to different chaperonin molecules ("cycling") during a folding reaction suggests that chaperonins function by unfolding aberrantly folded molecules, allowing them multiple opportunities to reach the native state in bulk solution. Here we show that the cycling of alpha-tubulin by cytosolic chaperonin (c-cpn) can be uncoupled from the action of cofactors required to complete the folding reaction. This results in the accumulation of folding intermediates which are chaperonin-bound, stable, and quasi-native in that they bind GTP nonexchangeably. We present evidence that these intermediates can be generated without the target protein leaving c-cpn. These data show that, in contrast to prevailing models, target proteins can maintain, and possibly acquire, significant native-like structure while chaperonin-bound.
伴侣蛋白已知可促进蛋白质折叠，但其作用机制尚未完全明确。在折叠反应过程中，目标蛋白从不同的伴侣蛋白分子上释放并重新结合（“循环”），这一事实表明伴侣蛋白通过展开异常折叠的分子发挥作用，使它们有多次机会在大量溶液中达到天然状态。在此我们表明，胞质伴侣蛋白（c-cpn）介导的α-微管蛋白的循环可以与完成折叠反应所需的辅助因子的作用解偶联。这导致了与伴侣蛋白结合的折叠中间体的积累，这些中间体是稳定的且接近天然状态，因为它们以不可交换的方式结合GTP。我们提供的证据表明，这些中间体可以在目标蛋白不离开c-cpn的情况下产生。这些数据表明，与主流模型相反，目标蛋白在与伴侣蛋白结合时可以维持并可能获得显著的类似天然的结构。
