Insights into Mechanisms of Amyloid Toxicity:  Molecular Dynamics Simulations of the Amyloid andbeta-peptide (Aandbeta) and Islet Amyloid Polypeptide (IAPP)

Aggregation of proteins into amyloid deposits is a common feature among dozens of diseases. Two such diseases that feature amyloid deposits are Alzheimer's disease (AD) and type 2 diabetes (T2D). AD toxicity has been associated with the aggregation and accumulation of the amyloid β-peptide (Aβ); Aβ exerts its toxic effects through interactions with neuronal cell membranes. A characteristic feature of T2D is the deposition of the islet amyloid polypeptide (IAPP) in the pancreatic islets of Langerhans. It is currently unknown if IAPP aggregation is a cause or consequence of T2D, but it does lead to β-cell dysfunction and death, exacerbating the effects of diabetes. Characterizing the fundamental interactions between both Aβ and IAPP with lipid membranes and in solution will give greater insight into mechanisms of toxicity exhibited by amyloid proteins. In this work, molecular dynamics (MD) simulations were used to study the secondary, tertiary, and quatnary structure of Aβ and IAPP, in addition to peptide-membrane interactions and membrane perturbation as independently caused by both peptides. Studies were conducted to address the following questions: (1) what influence do solution conditions and oxidation state have on monomeric Aβ] (2) how and in what way does monomeric Aβ interact with model lipid membranes and what role does sequence play on these peptide-membrane interactions; (3) can MD simulations be utilized to understand Aβ tetramer formation, rearrangement, and tetramer-membrane interactions; (4) how does IAP interact with model membranes and how does that vary from non-toxic (rat) IAPP peptide-membrane interactions. These studies led to conclusions that showed variance in lipid affinity and degree of perturbation as based on peptide sequence, in addition to insight into the type of perturbation caused to membranes by these amyloid peptides. Understanding the differences in peptide-membrane interactions of amyloidogenic and non-amyloidogenic (rat) peptides gave insight into the overall mechanism of amyloidogenicity, leading to the detection of specific amino acids essential in peptide-membrane perturbation. These residues can then be targeted for novel therapeutic design to attenuate the perturbation and potential cell death as caused by these peptides.