Effects of perturbation of the hydrophobic coiled-coil core on the thermal transition process of α-helical self-assembling peptides with α-β conformational transition capability

We designed a 29-residue peptide (CCP1) with helical nanofiber-forming ability, in which the interface of the coiled-coil motif consists only of hydrophobic residues, and peptides with histidine residues substituted in the hydrophobic core (CCP2 and CCP3), and analyzed the effects of perturbations caused by the substitutions on the intermolecular association and conformational transitions. Based on the results of atomic force microscopy and circular dichroism measurements, it was found that CCP1 and CCP2 form α-helical fibers under pH 4, while CCP3 adopts the α-helix structure but lacks the association ability. Furthermore, the heating processes of CCP1 and CCP2 were followed by using spectroscopic, thermal, and morphological techniques, and it was observed that CCP1 undergoes an irreversible structural transition from α-helical to β-sheet fibers with a high degree of cooperativity, while a more gradual or non-cooperative structural transition was observed in CCP2. These results indicate that the introduction of histidine residues in the hydrophobic core significantly affects the intermolecular interactions and the rate of structural transition, providing a new design principle for the development of functional nanomaterials with biocompatibility.