Decongested 2D IR Spectra Reveal N-Terminal Helices in Amyloid Oligomers Associated with Type 2 Diabetes

Oligomeric peptides are implicated in amyloidosis, yet only a few atomic structures of amyloid oligomers have been identified. Recently, we reported an atomic structural model of human islet amylin polypeptide (hIAPP) oligomer [Shivani, S. T.; et al.Proc. Natl. Acad. Sci. U.S.A.2026, 123, e2528103123.]. The model was generated by trapping the oligomers with three alanine substitutions in a sequence termed 3A-hIAPP. These substitutions neither impact the physiologically critical β-sheet region of hIAPP nor the cytotoxicity and oligomer size measured through biochemical assays. However, their effect on the structure of the N-terminal helices could not be assessed. By modifying our 2D IR spectrometer, we interwove the acquisition of multiple pulse sequences, enabling waiting-time-dependent spectra of hIAPP oligomers to be measured during protein aggregation. Spectra acquired at a waiting time of 1.2 ps are decongested of disordered structures, revealing features originating from the oligomeric N-terminal α-helix and the adjacent kink and disulfide-loop regions. The spectra of hIAPP oligomers closely match those of 3A-hIAPP, strengthening the structural relevance of our atomic model for hIAPP oligomers. These findings also establish a workflow for testing and generating atomic structures of hIAPP oligomers associated with early-onset type 2 diabetes and for oligomers from other amyloid diseases.