Cheng Kai, Wu Qiong, Zhang Zeting, Pielak Gary J, Liu Maili, Li Conggang
Key Laboratory of Magnetic Resonance in Biological Systems State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan Collaborative Innovation Center of Chemistry for Life Sciences, Wuhan, Institute of Physics and Mathematics Chinese Academy of Sciences, Wuhan, 430071, P. R. China.
Department of Chemistry Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, Chapel Hill, NC, 27599-3290, USA.
Chemphyschem. 2018 Dec 19;19(24):3350-3355. doi: 10.1002/cphc.201800857. Epub 2018 Nov 13.
Proteins encounter crowded and confined macromolecular milieus in living cells. Simple theory predicts that both environments entropically stabilize proteins if only hard-core repulsive interactions are considered. Recent studies show that chemical interactions between the surroundings and the test protein also play key roles such that the overall effect of crowding or confinement is a balance of hard-core repulsions and chemical interactions. There are, however, few quantitative studies. Here, we quantify the effects of crowding and confinement on the equilibrium unfolding thermodynamics of a model globular protein, KH1. The results do not agree with predictions from simple theory. KH1 is stabilized by synthetic-polymer crowding agents but destabilized by confinement in reverse micelles. KH1 is more entropically stabilized and enthalpically destabilized in concentrated solutions of the monomers than it is in solutions of the corresponding polymers. When KH1 is confined in reverse micelles, the temperature of maximum stability decreases, the melting temperature decreases, and the protein is entropically destabilized and enthalpically stabilized. Our results show the importance of chemical interactions to protein folding thermodynamics and imply that cells utilize chemical interactions to tune protein stability.
在活细胞中，蛋白质会处于拥挤且受限的大分子环境中。简单理论预测，如果仅考虑硬核排斥相互作用，那么这两种环境都会在熵的层面上使蛋白质稳定。近期研究表明，周围环境与受试蛋白质之间的化学相互作用也起着关键作用，以至于拥挤或受限的总体效应是硬核排斥与化学相互作用的平衡。然而，定量研究却很少。在此，我们量化了拥挤和受限对一种球状模型蛋白KH1平衡去折叠热力学的影响。结果与简单理论的预测并不一致。KH1在合成聚合物拥挤剂作用下会得到稳定，但在反胶束中的受限状态下会变得不稳定。与相应聚合物的溶液相比，KH1在单体的浓溶液中熵稳定性更高而焓稳定性更低。当KH1被限制在反胶束中时，最大稳定性温度降低，解链温度降低，并且蛋白质在熵上变得不稳定而在焓上变得稳定。我们的结果表明了化学相互作用对蛋白质折叠热力学的重要性，并暗示细胞利用化学相互作用来调节蛋白质稳定性。
