Human islet amyloid polypeptide (hIAPP) is a highly amyloidogenic peptide found in pancreatic islets of type-2 diabetes (T2D) patients. Under certain conditions, hIAPP is able to form amyloid fibrils that play a role in the progression of T2D. hIAPP is synthesized in the β-cell of the pancreas and stored in the secretory granules before being released into the extracellular compartment. It has been suggested that natural stabilizing agents, such as insulin or zinc present in the secretory granules with hIAPP could prevent hIAPP fibril formation. The difference in the amino acid sequences of IAPP among species strongly correlates with amyloidogenicity and toxicity. The residue histidine at position 18 is known to be important in modulating the fibril formation, membrane leakage and toxicity. In this study, we have synthesized four analogues of hIAPP (H18R-IAPP, H18K-IAPP, H18A-IAPP and H18E-IAPP) and characterized their aggregation with either insulin or zinc in order to determine the effect of the residue-18 on the insulin-IAPP and zinc-IAPP interactions using a variety of biophysical experiments including thioflavin-T fluorescence, transmission electron microscopy imaging, circular dichroism, and NMR spectroscopy. We show that insulin reduced hIAPP fibril formation both in solution and in the presence of membrane and hIAPP-membrane damage and that the interactions are somewhat mediated by the residue-18. In addition, our results reveal that zinc affects the process of hIAPP fibril formation in solution but not in the presence of membrane. Our results indicate that the nature of the residue-18 is important for zinc binding. Based on this observation, we hypothesize that zinc binds to the residues in the N-terminal region of hIAPP, which is not accessible in the presence of membrane due to its strong interaction with lipids.

人胰岛淀粉样多肽 (hIAPP) 是一种在 2 型糖尿病 (T2D) 患者的胰岛中发现的高度淀粉样肽。在某些条件下，hIAPP 能够形成淀粉样原纤维，在 T2D 的进展中发挥作用。hIAPP 在胰腺的 β 细胞中合成，并在释放到细胞外区室之前储存在分泌颗粒中。已经提出，天然稳定剂，例如存在于具有 hIAPP 的分泌颗粒中的胰岛素或锌，可以防止 hIAPP 原纤维形成。物种间 IAPP 氨基酸序列的差异与淀粉样蛋白原性和毒性密切相关。已知第 18 位的残基组氨酸在调节原纤维形成、膜渗漏和毒性方面很重要。在这项研究中，我们已经合成了 hIAPP 的四种类似物（H18R-IAPP、H18K-IAPP、H18A-IAPP 和 H18E-IAPP），并表征了它们与胰岛素或锌的聚集，以确定残基 18 对胰岛素-IAPP 和锌-IAPP 相互作用使用各种生物物理实验，包括硫代黄素-T 荧光、透射电子显微镜成像、圆二色性和核磁共振光谱。我们表明，胰岛素在溶液中和存在膜和 hIAPP 膜损伤的情况下都减少了 hIAPP 原纤维的形成，并且这种相互作用在某种程度上是由残基 18 介导的。此外，我们的结果表明，锌会影响 hIAPP 原纤维在溶液中的形成过程，但在膜存在的情况下不会。我们的结果表明残基 18 的性质对锌结合很重要。