Louros Nikolaos N, Tsiolaki Paraskevi L, Baltoumas Fotis A, Chryssikos Georgios D, Gionis Vassilis, Hamodrakas Stavros J, Iconomidou Vassiliki A
Section of Cell Biology and Biophysics, Department of Biology, School of Sciences, National and Kapodistrian University of Athens, Panepistimiopolis, Athens 157 01, Greece.
Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Athens 116 35, Greece.
J Struct Biol. 2017 Aug;199(2):140-152. doi: 10.1016/j.jsb.2017.06.002. Epub 2017 Jun 14.
Human islet amyloid polypeptide (hIAPP) is the major protein component of extracellular amyloid deposits, located in the islets of Langerhans, a hallmark of type II diabetes. The underlying mechanisms of IAPP aggregation have not yet been clearly defined, although the highly amyloidogenic sequence of the protein has been extensively studied. Several segments have been highlighted as aggregation-prone regions (APRs), with much attention focused on the central 8-17 and 20-29 stretches. In this work, we employ micro-Raman spectroscopy to identify specific regions that are contributing to or are excluded from the amyloidogenic core of IAPP amyloid fibrils. Our results demonstrate that both the N-terminal region containing a conserved disulfide bond between Cys residues at positions 2 and 7, and the C-terminal region containing the only Tyr residue are excluded from the amyloid core. Finally, by performing detailed aggregation assays and molecular dynamics simulations on a number of IAPP variants, we demonstrate that point mutations within the central APRs contribute to the reduction of the overall amyloidogenic potential of the protein but do not completely abolish the formation of IAPP amyloid fibrils.
人胰岛淀粉样多肽（hIAPP）是细胞外淀粉样沉积物的主要蛋白质成分，位于朗格汉斯胰岛中，是II型糖尿病的一个标志。尽管该蛋白质的高度淀粉样变序列已被广泛研究，但IAPP聚集的潜在机制尚未明确界定。几个片段已被突出为易于聚集的区域（APR），其中大部分注意力集中在中央的8 - 17和20 - 29片段。在这项工作中，我们采用显微拉曼光谱来识别有助于IAPP淀粉样纤维形成或被排除在其淀粉样变核心之外的特定区域。我们的结果表明，包含第2位和第7位半胱氨酸残基之间保守二硫键的N端区域以及包含唯一酪氨酸残基的C端区域都被排除在淀粉样核心之外。最后，通过对多个IAPP变体进行详细的聚集测定和分子动力学模拟表明，中央APR内的点突变有助于降低蛋白质的整体淀粉样变潜力，但并未完全消除IAPP淀粉样纤维的形成。
