Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180, United States.
J Am Chem Soc. 2011 Sep 28;133(38):15157-64. doi: 10.1021/ja2054572. Epub 2011 Sep 2.
We study the equilibrium folding/unfolding thermodynamics of a small globular miniprotein, the Trp cage, that is confined to the interior of a 2 nm radius fullerene ball. The interactions of the fullerene surface are changed from nonpolar to polar to mimic the interior of the GroEL/ES chaperonin that assists proteins to fold in vivo. We find that nonpolar confinement stabilizes the folded state of the protein due to the effects of volume reduction that destabilize the unfolded state and also due to interactions with the fullerene surface. For the Trp cage, polar confinement has a net destabilizing effect that results from the stabilizing confinement and the competitive exclusion effect that keeps the protein away from the surface hydration shell and stronger interactions between charged side chains in the protein and the polar surface that compete against the formation of an ion pair that stabilizes the protein folded state. We show that confinement effects due to volume reduction can be overcome by sequence-specific interactions of the protein side chains with the encapsulating surface. This study shows that there is a complex balance among many competing effects that determine the mechanism of GroEL chaperonin in enhancing the folding rate of polypeptide inside its cavity.
我们研究了一种小型球状小分子蛋白——色氨酸笼（Trp cage）在 2nm 半径富勒烯球内部的平衡折叠/去折叠热力学。通过改变富勒烯表面的相互作用从非极性到极性，模拟了 GroEL/ES 伴侣蛋白在体内辅助蛋白质折叠的内部环境。我们发现，非极性限制由于体积减小的影响使去折叠状态不稳定，并且由于与富勒烯表面的相互作用，从而稳定了蛋白质的折叠状态。对于色氨酸笼，极性限制具有净去稳定效应，这是由于稳定限制和竞争排斥效应的共同作用，使蛋白质远离表面水合壳，以及蛋白质带电侧链与极性表面之间更强的相互作用，竞争形成稳定蛋白质折叠状态的离子对。我们表明，由于体积减小而导致的限制效应可以通过蛋白质侧链与封装表面的序列特异性相互作用来克服。这项研究表明，在确定 GroEL 伴侣蛋白在增强其腔内部多肽折叠速率的机制中，有许多竞争效应之间存在着复杂的平衡。
