Amyloid versus Hydrogel Fibrillar Architectures in Short Amyloidogenic Peptides: Structural Insights at Amino Acid Resolution

Abstract Amyloid peptides self-assemble into either pathogenic insoluble fibrils or functional hydrogel networks, yet their molecular-level structural differences remain poorly understood. This study utilized isotope-edited Infrared (IR) and vibrational circular dichroism (VCD) spectroscopies to compare the residue-level structures of amyloid and hydrogel fibrils formed by short peptide fragments from α-synuclein (SYN), human islet amyloid polypeptide (hIAPP), and Lactoferrin (LAN). Results showed that structural differences depend heavily on the peptide sequence. For SYN, short, bundled amyloid fibrils form in-registry parallel β-sheets, whereas long hydrogel networks contain parallel β-sheets with a minor C-terminal helical turn, exhibiting opposite supramolecular chirality. Similarly, IAP assemblies display opposite chirality and parallel β-sheets, but distinct coupling interactions reveal different local packing arrangements. Conversely, both LAN fibril types show identical long morphologies, matching supramolecular chirality, and parallel β-sheets mixed with N-terminal β-turn/loop involvement. Overall, isotope-edited IR and VCD analysis confirm that amyloid and hydrogel fibrils possess distinct molecular arrangements, twists, and morphologies dictated by their secondary structure in the corresponding fibril forms. By linking macroscopic morphology to residue-level structure and supramolecular organization, these findings provide critical insights for designing targeted amyloidosis therapies and functional biomaterials.