Analysis of Prairie Vole Amylin Reveals the Importance of the N-Terminus and Residue 22 in Amyloidogenicity and Cytotoxicity

Amyloid formation by amylin contributes to beta-cell dysfunction in type 2 diabetes. The features that control the amyloidogenicity and toxicity of amylin are not understood. Not all species form islet amyloid, and its presence or absence correlates with the in vitro behavior of the polypeptide. Rats do not develop type 2 diabetes or islet amyloid, and rat amylin is non-amyloidogenic, except at very high concentrations. This has led to the notion that rodent amylins are nonamyloidogenic. Prairie vole amylin has an unusual sequence compared to those of human and rat amylin, including nonconservative Lys-1 to Glu and Asn-22 to Gly substitutions. The first reduces the net charge on the peptide, while the second disrupts a potential network of side chain hydrogen bonds in the amyloid fiber, a so-called Asn ladder. The prairie vole polypeptide forms amyloid more slowly than human amylin and is considerably less cytotoxic. An Asn-22 to Gly substitution in human amylin significantly reduces toxicity, increasing the effective concentration of amylin required to reach 50% toxicity by >7-fold, but has modest effects on the time to form amyloid. A Lys-1 to Glu replacement has a weaker effect but does reduce toxicity relative to that of human amylin, without having a significant impact on the time to form amyloid. The effect of the Lys-1 to Glu substitution on amyloid kinetics is more significant in Tris buffer than in phosphate-buffered saline. This work demonstrates that the N-terminus of amylin plays a role in modulating toxicity and highlights the key role of position 22.