Lapidus Lisa J, Eaton William A, Hofrichter James
Laboratory of Chemical Physics, Building 5, 5 Center Drive, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, USA.
J Mol Biol. 2002 May 24;319(1):19-25. doi: 10.1016/S0022-2836(02)00193-6.
To investigate the dynamic flexibility of the coil state of a helix-forming peptide the end-to-end contact rate was determined. Nanosecond optical excitation of tryptophan at one end of a 22 residue, alanine peptide populates a long-lived triplet state which is quenched upon close contact with a cyclic disulfide attached to the opposite end. Analysis of the decay of the triplet population using a two-state model for helix formation yields the diffusion-limited end-to-end contact rate of the coil state of the peptide as well as the helix-->coil and coil-->helix rates. The helix-coil rates are very similar to those previously measured in laser temperature-jump experiments. The end-to-end contact rate of 1.1 x 10(7) s(-1) in the coil state is tenfold faster than the rate for a disordered peptide with threonine substituted for alanine and, somewhat surprisingly, is about twice the rate for a disordered glycine-containing peptide. These differences are discussed in terms of the theory of Szabo, Schulten and Schulten. The rates should provide important new benchmarks for testing the accuracy of atomistic molecular dynamics simulations.
为了研究形成螺旋的肽的卷曲状态的动态柔韧性，测定了端对端接触速率。对一个由22个残基组成的丙氨酸肽一端的色氨酸进行纳秒级光激发，会产生一个长寿命三重态，当与连接在另一端的环二硫键紧密接触时，该 三重态会被淬灭。使用用于螺旋形成的双态模型对三重态布居的衰减进行分析，可得出肽的卷曲状态的扩散限制端对端接触速率以及螺旋→卷曲和卷曲→螺旋速率。螺旋 - 卷曲速率与之前在激光温度跳跃实验中测得的速率非常相似。卷曲状态下端对端接触速率为1.1×10⁷ s⁻¹，比用苏氨酸取代丙氨酸的无序肽的速率快十倍，而且有些令人惊讶的是，大约是含甘氨酸的无序肽速率的两倍。根据萨博、舒尔滕和舒尔滕的理论对这些差异进行了讨论。这些速率应为测试原子分子动力学模拟的准确性提供重要的新基准。
