Qiu Linlin, Zachariah Cherian, Hagen Stephen J
University of Florida, Physics Department, P.O. Box 118440, Gainesville, Florida 32611-8440, USA.
Phys Rev Lett. 2003 Apr 25;90(16):168103. doi: 10.1103/PhysRevLett.90.168103.
Theory indicates that at least some proteins will undergo a rapid and unimpeded collapse, like a disorganized hydrophobic chain, prior to folding. Yet experiments continue to find signs of an organized, or barrier-limited, collapse in even the fastest (approximately mus) folding proteins. Does the kinetic barrier represent a signature of the equilibrium "foldability" of these molecules? We have measured the rate of chain contraction in two nonfolding analogs of a very fast-collapsing protein. We find that these chains contract on the same time scale (approximately 10(-5)s) as the natural protein, and both pass over an energetic barrier at least as large as that encountered by the protein. The equilibrium foldability of the native structure therefore does not alone determine the dynamics of collapse; even the disordered chains contract approximately 1000x slower than expected for an ideal chain.
理论表明，至少某些蛋白质在折叠之前会像无序的疏水链一样经历快速且不受阻碍的折叠。然而，实验不断发现，即使是折叠速度最快（约微秒级）的蛋白质，也存在有序或受屏障限制的折叠迹象。动力学屏障是否代表了这些分子平衡“可折叠性”的特征呢？我们测量了一种折叠速度非常快的蛋白质的两种非折叠类似物的链收缩速率。我们发现，这些链的收缩时间尺度（约10^(-5)秒）与天然蛋白质相同，并且两者都越过了至少与蛋白质所遇到的能量屏障一样大的能量屏障。因此，天然结构的平衡可折叠性并不能单独决定折叠的动力学；即使是无序的链，其收缩速度也比理想链预期的慢约1000倍。
