Inter-species cross-seeding: stability and assembly of rat-human amylin aggregates.

Workalemahu M Berhanu,Ulrich H E Hansmann

doi:10.1371/journal.pone.0097051

Abstract

Diseases such as type 2 diabetes, Alzheimer’s and Parkinson’s share as common feature the accumulation of mis-folded disease-specific protein aggregates into fibrillar structures, or plaques. These fibrils may either be toxic by themselves, or act as reservoirs for smaller cytotoxic oligomers. This suggests to investigate molecules as potential therapeutics that either reduce fibril formation or increase fibril stability. One example is rat amylin, which can inhibit aggregation of human amylin, a hallmark of type 2 diabetes. In the present paper, we use molecular dynamics to compare the stability of various preformed aggregates, built out of either human amylin, rat amylin, or mixtures of both. We considered two types of fibril-like oligomers: a single-layer in-register conformation, and a double-layer conformation in which the first U-shaped layer consists of rat amylin and the second layer of human amylin. Our results explain the weak amyloid-inhibiting properties of rat amylin and suggest that membrane leakage due to pore formation is responsible for the toxicity of rat amylin observed in a recent experiment. Together, our results put in question the use of rat amylin or the similar FDA approved drug pramlintide as an inhibitor of human amylin aggregation. They also point to mixed human-rat amylin fibril-like oligomers as possible model-systems for studies of amyloid formation that involve cross-species transmission.

Highlights

In human amyloid diseases, protein mis-folding triggers the formation of amyloid oligomers and fibers that can cause cell death leading to either localized or systemic organ failure [1]
We have investigated in silico the stability of various rat and human amylin aggregates
We have identified the L13ANFL17 motif of hydrophobic residues in the b1 region of amylin [51] as crucial for the stabilization of the cross-seeded aggregates. This insight might be useful for the design of aggregation inhibitors that improve upon the weak aggregation-inhibiting properties of rat amylin: computational screening of fiber-binding compounds could reveal small organic molecules or peptide-mimetics that stabilize the b-sheet regions reducing in this way amylin toxicity in type-2 diabetes

Summary

Introduction

Protein mis-folding triggers the formation of amyloid oligomers and fibers that can cause cell death leading to either localized or systemic organ failure [1]. The main toxic species are not mature fibers but amyloid oligomers [10], [11], with the fibrils potentially acting as reservoirs for the toxic oligomers. This suggests as potential therapeutics molecules that stabilize fibers and shift the equilibrium from smaller, toxic entities towards the fibrillar state [12], [13]. A candidate for such molecules is rat amylin, which due to its high sequence similarity [14] binds strongly to human amylin, but is not amyloidogenic under physiological conditions [15] (and rats do not develop type 2 diabetes [16,17]). Mixing equal molar concentrations of rat with human amylin leads to a deposition of the non-aggregating rat amylin onto human amylin fibrils resulting in a weak aggregation inhibitor activity [18]

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