Laboratory of Chemical Physics, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA.
Biophys J. 2009 Dec 2;97(11):2948-57. doi: 10.1016/j.bpj.2009.08.041.
Islet amyloid polypeptide (amylin) is the main component in amyloid deposits formed in type II diabetes. We used triplet quenching to probe the dynamics of contact formation between the N-terminal disulfide loop and a C-terminal tryptophan in monomeric amylins from human and rat. Quenching rates measured in the absence of denaturant are four times larger than those in 6 M guanidinium chloride, indicating a decrease in the average end-to-end distance (collapse) at low denaturant concentrations. We were surprised to find an even greater (sevenfold) increase in quenching rates on removal of denaturant for a hydrophilic control peptide containing the disulfide loop compared to the same peptide without the loop (twofold change). These results suggest that collapse is driven by backbone-backbone and backbone-side chain interactions involving the disulfide loop portion of the chain rather than by the formation of side-chain hydrophobic contacts. Molecular dynamics simulations of the control peptide show that the collapse results from hydrogen-bonding interactions between the central residues of the chain and the disulfide loop. The quenching experiments also indicate that the monomer of the human, amyloidogenic form of amylin is more compact than the rat form, which does not form amyloid. We discuss these newly observed differences between human and rat amylin in solution and their possible relation to aggregation and to the physiological function of amylin binding to the calcitonin receptor.
胰岛淀粉样多肽（amylin）是在 2 型糖尿病中形成的淀粉样沉积物的主要成分。我们使用三聚体猝灭来探测人源和鼠源单体 amylin 中 N 端二硫环和 C 端色氨酸之间接触形成的动力学。在没有变性剂的情况下测量的猝灭速率比在 6 M 盐酸胍中测量的速率大四倍，这表明在低变性剂浓度下平均末端到末端距离（崩溃）减小。令人惊讶的是，与不含环的相同肽（两倍变化）相比，对于含有二硫环的亲水性对照肽，在除去变性剂时猝灭速率甚至增加了（七倍）。这些结果表明，崩溃是由涉及链的二硫环部分的主链-主链和主链-侧链相互作用驱动的，而不是由形成侧链疏水接触驱动的。对照肽的分子动力学模拟表明，崩溃是由链的中心残基与二硫环之间的氢键相互作用引起的。猝灭实验还表明，人源淀粉样蛋白的单体比不形成淀粉样蛋白的鼠源形式更紧凑。我们讨论了在溶液中观察到的这些新的人源和鼠源 amylin 之间的差异及其与聚集和 amylin 与降钙素受体结合的生理功能的可能关系。
