Insight into Cross-Amyloid Interactions and Morphologies: Molecular Dynamics Simulations of Model Peptide Fragments of Amyloid-β (Aβ16-22) and Islet Amyloid Polypeptide (IAPP20-29)

Amyloid-beta (A{beta}) and islet amyloid polypeptide (IAPP) are small peptides, classified as amyloids, that have the potential to self-assemble and form cytotoxic species, such as small soluble oligomers and large insoluble fibrils. The formation of A{beta} aggregates facilitates the progression of Alzheimers disease (AD), while IAPP aggregates induce pancreatic {beta}-cell apoptosis, leading to exacerbation of Type 2 diabetes (T2D). Cross-amyloid interactions between A{beta} and IAPP have been described both in vivo and in vitro, implying the role of A{beta} or IAPP as modulators of cytotoxic self-aggregation of each peptide, and suggesting that A{beta}-IAPP interactions are a potential molecular link between AD and T2D. Using molecular dynamics simulations, "hot spot" regions of the two peptides were studied to understand the formation of hexamers in a heterogenous and homogenous peptide-containing environment. Systems of only A{beta}(16-22) peptides formed antiparallel, {beta}-barrel-like structures, while systems of only IAPP(20-29) peptides formed stacked, parallel beta strands and had relatively unstable aggregation structures after 2 s of simulation time. Systems containing both A{beta} and IAPP (1:1 ratio) hexamers showed antiparallel, {beta}-barrel-like structures, with an interdigitated arrangement of A{beta}(16-22) and IAPP(20-29). These {beta}-barrel structures have features of cytotoxic amyloid species identified in previous literature. Ultimately, this work seeks to provide atomistic insight into both the mechanism behind cross-amyloid interactions and structural morphologies of these toxic amyloid species. Statement of SignificanceMolecular knowledge, biophysical characterization, structural morphologies, and formation pathways of amyloid oligomers - specifically low-molecular weight, cross-amyloid oligomers - remain preliminary and undefined. Characterizing interactions between homogenous and heterogenous amyloid oligomers is of great interest given that certain oligomer morphologies contribute to cytotoxicity, eventually resulting in comorbid diseases such as Alzheimers disease (AD) and Type 2 Diabetes Mellitus (T2DM). Utilizing model systems (e.g., fragments of full-length peptides) and molecular dynamics (MD) simulations to probe the biophysical underpinnings of cross-amyloid oligomer structures is the first step in understanding the dynamics, stability, and potential modes of cytotoxicity of these species, providing important insights into targetable biomolecular structures.