Forced amyloidogenic cooperativity of structurally incompatible peptide segments: Fibrillization behavior of highly aggregation-prone A-chain fragment of insulin coupled to all-L, and alternating L/D octaglutamates.

Aggregation of proteins into amyloid fibrils is driven by interactions between relatively small amyloidogenic segments. The interplay between aggregation-prone and aggregation-resistant fragments within a single polypeptide chain remains obscure. Here, we examine fibrillization behavior of two chimeric peptides, ACCE and ACCE, in which the highly amyloidogenic fragment of insulin (ACC) is extended by an octaglutamate segment composed of all-L (E), or alternating L/D residues (E).

Reversible Freeze-Induced β-Sheet-to-Disorder Transition in Aggregated Homopolypeptide System.

Conformational transitions involving aggregated proteins or peptides are of paramount biomedical and biotechnological importance. Here, we report an unusual freeze-induced structural reorganization within a β-sheet-rich ionic coaggregate of poly(l-lysine), PLL, and poly(l-glutamic acid), PLGA. Freezing aqueous suspensions of the PLL-PLGA β-aggregate in the presence of low concentrations of salt (NaBr) induces an instantaneous β-sheet-to-disorder transition, as probed by infrared spectroscopy in the amide I' band region.