Physical Chemistry I - Biophysical Chemistry, Department of Chemistry, TU Dortmund University, Otto-Hahn Str. 6, D-44227, Dortmund, Germany.
Biophys Chem. 2010 Aug;150(1-3):73-9. doi: 10.1016/j.bpc.2010.01.006. Epub 2010 Jan 28.
Aggregation of human islet amyloid polypeptide (hIAPP) into cytotoxic beta-sheet oligomers and amyloid plaques is considered a key event in pancreatic beta-cell degeneration in type 2 diabetes (T2D). hIAPP is synthesized in the pancreatic beta-cells and it is stored, co-processed in the secretory granules, and co-secreted to the extracellular matrix together with insulin. In vivo, hIAPP aggregation may start and proceed at the water-cell membrane interface and anionic lipid membranes strongly enhance the process of hIAPP fibrillization which is causally linked to membrane disintegration and cell degeneration. In this study we explored the amyloidogenic propensity and conformational properties of hIAPP in the presence of negatively charged membrane (DOPC/DOPG phospholipid bilayers) surfaces upon addition of two recently designed potent hIAPP-derived inhibitors of hIAPP amyloidogenesis, the hexapeptide NF(N-Me)GA(N-Me)IL (NFGAIL-GI) and the 37-residue non-amyloidogenic hIAPP analog [(N-Me)G24, (N-Me)I26]-IAPP (IAPP-GI). For comparison, the effects of insulin, which is a natively occurring hIAPP aggregation inhibitor, rat IAPP (rIAPP), which is a natively non-amyloidogenic hIAPP analog, and the hIAPP amyloid core peptide hIAPP(22-27) or NFGAIL were also studied. The aim of our study was to test whether and how the above peptides which have been shown to completely block or suppress hIAPP amyloidogenesis in bulk solution in vitro would also affect these processes in the presence of lipid membranes. To this end, attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) was applied. We find that IAPP-GI, NFGAIL-GI, insulin, and rIAPP are potent inhibitors of hIAPP fibrillization. Importantly, our data also suggest that the hetero-complexes of IAPP-GI, rIAPP, and insulin with hIAPP although non-amyloidogenic per se are still able to adsorb at the lipid membrane. By contrast, in the presence of NFGAIL-GI, interaction of hIAPP with the lipid membrane is completely abolished, consistent with NFGAIL-GI mediated sequestration of hIAPP via hetero-complexation in the aqueous phase mainly accounting for the observed strong effect of NFGAIL-GI on hIAPP fibrillogenesis at the lipid membrane interface. Finally, our studies show that once hIAPP is fibrillized at the water-lipid membrane interface with fibrils being attached to the lipid membrane, it cannot be disaggregated by all above peptides.
人胰岛淀粉样多肽（hIAPP）聚集形成细胞毒性β-折叠寡聚物和淀粉样斑块被认为是 2 型糖尿病（T2D）中胰岛β细胞退化的关键事件。hIAPP 在胰腺β细胞中合成，与胰岛素一起在分泌颗粒中储存、共同加工，并共同分泌到细胞外基质中。在体内，hIAPP 的聚集可能在水-细胞膜界面开始并进行，阴离子脂质膜强烈促进 hIAPP 原纤维形成的过程，这与膜崩解和细胞退化有关。在这项研究中，我们在添加两种最近设计的强效 hIAPP 淀粉样形成抑制剂，六肽 NF（N-Me）GA（N-Me）IL（NFGAIL-GI）和 37 残基非淀粉样形成 hIAPP 类似物[（N-Me）G24，（N-Me）I26]-IAPP（IAPP-GI）的情况下，研究了 hIAPP 在带负电荷的膜（DOPC/DOPG 磷脂双层）表面上的淀粉样倾向和构象特性。为了进行比较，还研究了胰岛素、天然存在的 hIAPP 聚集抑制剂、天然非淀粉样形成的大鼠 IAPP（rIAPP）、hIAPP 淀粉样核心肽 hIAPP（22-27）或 NFGAIL 的影响。我们研究的目的是测试上述肽是否以及如何在体外完全阻断或抑制 hIAPP 淀粉样形成，并且还会影响存在脂质膜时的这些过程。为此，应用了衰减全反射傅里叶变换红外光谱（ATR-FTIR）。我们发现 IAPP-GI、NFGAIL-GI、胰岛素和 rIAPP 是 hIAPP 原纤维形成的有效抑制剂。重要的是，我们的数据还表明，尽管本身是非淀粉样形成的，但 IAPP-GI、rIAPP 和胰岛素与 hIAPP 的异质复合物仍然能够在脂质膜上吸附。相比之下，在 NFGAIL-GI 的存在下，hIAPP 与脂质膜的相互作用完全被废除，这与 NFGAIL-GI 通过在水相中介导异质复合物化来隔离 hIAPP 一致，这主要导致了 NFGAIL-GI 对 hIAPP 在脂质膜界面上的原纤维形成的强烈影响。最后，我们的研究表明，一旦 hIAPP 在水-脂质膜界面上形成原纤维并且原纤维附着在脂质膜上，就不能被所有上述肽解聚。
