Specific Mutations Alter Fibrillation Kinetics, Fiber Morphologies, and Membrane Interactions of Pentapeptides Derived from Human Calcitonin

Abstract

Protein misfolding and fibrillation are fundamental facets underlying a diverse group of amyloid disorders and diseases. The molecular factors responsible for amyloid protein toxicity and pathological consequences, however, are still not fully understood. The involvement of specific residues or sequence elements in fibril formation and the interactions of amyloid protein aggregates with membranes are believed to constitute two critical parameters contributing to amyloidogenesis and amyloid pathologies. This work aims to elucidate sequence determinants and membrane-protein interactions of five-residue peptide fragments derived from a core amyloidogenic sequence of human calcitonin. We show that single-residue mutations within the native pentapeptide sequence significantly modulate the kinetics of peptide self-assembly, alter beta-sheet organization between parallel and antiparallel arrangements, and modify fibrillar morphologies. We further demonstrate that hydrophobic or aromatic interactions are not prerequisites for peptide fiber formation. The experiments also disclose pronounced effects of lipid vesicles comprising cholesterol and negatively charged phospholipids on the rate of fibrillation and fiber structures formed by the short peptides. This work indicates that the structural and kinetic properties of peptide fibrils as well as lipid interactions of fibrillar species are interrelated and are significantly affected by specific residues within amyloid peptide sequences.