Department of Chemistry and Biochemistry , University of California , Santa Barbara , California 93106 , United States.
Department of Chemistry and Biochemistry , Rowan University , Glassboro , New Jersey 08028 , United States.
J Am Chem Soc. 2018 Aug 1;140(30):9685-9695. doi: 10.1021/jacs.8b05925. Epub 2018 Jul 23.
Protein aggregation is typically attributed to the association of homologous amino acid sequences between monomers of the same protein. Coaggregation of heterogeneous peptide species can occur, however, and is implicated in the proliferation of seemingly unrelated protein diseases in the body. The prion protein fragment (PrP) and human islet amyloid polypeptide (hIAPP) serve as an interesting model of nonhomologous protein assembly as they coaggregate, despite a lack of sequence homology. We have applied ion-mobility mass spectrometry, atomic force microscopy, circular dichroism, and high-level molecular modeling to elucidate this important assembly process. We found that the prion fragment not only forms pervasive hetero-oligomeric aggregates with hIAPP but also promotes the transition of hIAPP into its amyloidogenic β-hairpin conformation. Further, when PrP was combined with non-amyloidogenic rIAPP, the two formed nearly identical hetero-oligomers to those seen with hIAPP, despite rIAPP containing β-sheet breaking proline substitutions. Additionally, while rIAPP does not natively form the amyloidogenic β-hairpin structure, it did so in the presence of PrP and underwent a conformational transition to β-sheet in solution. We also find that PrP forms hetero-oligomers with the IAPP fragment but not with the "aggregation hot spot" IAPP fragment. PrP apparently induces IAPP into a β-hairpin structure within the PrP:IAPP heterodimer complex and then, through ligand exchange, catalytically creates the amyloidogenic β-hairpin dimer of IAPP in significantly greater abundance than IAPP does on its own. This is a new mechanistic model that provides a critical foundation for the detailed study of hetero-oligomerization and prion-like proliferation in amyloid systems.
蛋白质聚集通常归因于同一蛋白质单体中同源氨基酸序列的缔合。然而，异质肽物种的共聚集也会发生，并与体内看似无关的蛋白质疾病的增殖有关。朊病毒蛋白片段（PrP）和人胰岛淀粉样多肽（hIAPP）作为非同源蛋白质组装的有趣模型，尽管它们缺乏序列同源性，但它们会共聚集。我们应用离子淌度质谱、原子力显微镜、圆二色性和高级分子建模来阐明这个重要的组装过程。我们发现，朊病毒片段不仅与 hIAPP 形成普遍的异源寡聚体，还促进了 hIAPP 向其淀粉样β-发夹构象的转变。此外，当 PrP 与非淀粉样形成的 rIAPP 结合时，尽管 rIAPP 含有破坏β-折叠的脯氨酸取代，但两者形成的异源寡聚体与与 hIAPP 相似。此外，虽然 rIAPP 本身不会形成淀粉样β-发夹结构，但在 PrP 的存在下会形成，并且在溶液中发生构象转变为β-折叠。我们还发现 PrP 与 IAPP 片段形成异源寡聚体，但与“聚集热点”IAPP 片段不形成。PrP 显然在 PrP：IAPP 杂二聚体复合物中将 IAPP 诱导成β-发夹结构，然后通过配体交换，催化地以比 IAPP 自身更高的丰度产生淀粉样β-发夹二聚体的 IAPP。这是一个新的机制模型，为淀粉样系统中异源寡聚化和朊病毒样增殖的详细研究提供了重要基础。
