Inhibition of Human Amylin Amyloidogenesis by Human Amylin-Fragment Peptides: Exploring the Effects of Serine Residues and Oligomerization upon Inhibitory Potency.

To date, fragments from within the amyloidogenic-patch region of human amylin (hAM) have been shown to aggregate independently of the full-length peptide. In this study, we show that under certain conditions, both oligomers of NFGAILSS and the monomeric form are capable of inhibiting the aggregation of the full-length hAM sequence. The inhibition, rather than aggregate seeding, observed with the soluble portion of aged NFGAILSS solutions was particularly striking occurring at far substoichiometric levels. Apparently, the oligomer form of this fragment is responsible for inhibiting the transition from random coil to β-sheet or serves as a disaggregator of hAM β-oligomers. Sequential deletion of the serine residues from NFGAILSS results in a decrease of inhibition, indicating that these residues are important to the activity of this fragment. We, like others, observed instances of α-helix-like CD spectra prior to β-sheet formation as part of the amyloidogenesis pathway. The partially aggregated sample and the fragments studied display spectroscopic diagnostics, suggesting that they slow down the conversion of full-length hAM monomers to cytotoxic oligomers.