The effect of exposing a critical hydrophobic patch on amyloidogenicity and fibril structure of insulin

It is widely accepted that the formation of amyloid fibrils is one of the natural properties of proteins. The amyloid formation process is associated with a variety of factors, among which the hydrophobic residues play a critical role. In this study, insulin was used as a model to investigate the effect of exposing a critical hydrophobic patch on amyloidogenicity and fibril structure of insulin. Porcine insulin was digested with trypsin to obtain desoctapeptide-(B23-B30) insulin (DOI), whose hydrophilic C-terminal of B-chain was removed and hydrophobic core was exposed. The results showed that DOI, of which the ordered structure (predominantly α-helix) was markedly decreased, was more prone to aggregate than intact insulin. As to the secondary structure of amyloid fibrils, DOI fibrils were similar to insulin fibrils formed under acidic condition, whereas under neutral condition, insulin formed less polymerized aggregates by showing decreased β-sheet contents in fibrils. Further investigation on membrane damage and hemolysis showed that DOI fibrils induced significantly less membrane damage and less hemolysis of erythrocytes compared with those of insulin fibrils. In conclusion, exposing the hydrophobic core of insulin can induce the increase of amyloidogenicity and formation of higher-order polymerized fibrils, which is less toxic to membranes.