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Polymers and Self Assembly: From Biology to Nanomaterials Poster Session II
3-POS
Board 3
Subverting Amyloid Laws of Attraction: Inhibition of Fibril Assembly through Like-
Charge Repulsion
Andrei Alexandrescu
University of Connecticut, Storrs, USA
In amyloid structures like-charges are replicated along the one-dimensional lattice that
constitutes the fibril axis. Repulsion between like-charges should oppose fibril assembly. To
probe the role of charges in fibrillogenesis we have studied the pH-dependence of amylin, a
peptide hormone that forms amyloids in type 2 diabetes. Amylin has two ionizable sites: the
alpha-amino group at the N-terminus and His18. Our approach has been to look at the pH-
dependence of fibrillization kinetics, in variants that have only one of the two groups. The α-
amino group at the unstructured N-terminus of amylin has a pKa near 8.0, similar to random coil
models, and makes only small contributions. By contrast, His18, which participates in the
intermolecular β-sheet structure, has a pKa lowered to ~5.0 from the random coil value of 6.5.
His18 acts as an electrostatic switch, inhibiting aggregation in its charged state at acidic pH and
favoring fibrillization in its uncharged state at neutral pH. The presence of a charged side-chain
at position 18 affects fibril morphology and lowers amylin cytotoxicity towards a mouse model
of pancreatic β-cells. We exploited the principle that electrostatic repulsion interferes with fibril
formation to design peptide variants Arg1 and Arg2, which incorporate strings of four arginines
in the amylin amino acid sequence. The charge-loaded peptides fibrillize poorly on their own,
and inhibit fibril elongation of WT-amylin at physiological salt concentrations. The most
effective inhibitor Arg-1, inhibits WT-amylin fibril elongation rates with an IC50 of ~1 µM and
cytotoxicity with an IC50 of ~50 µM, comparable to other inhibitors reported in the literature.
These studies suggest that electrostatic interactions can be exploited to develop new types of
inhibitors of amyloid fibrillization and toxicity.