Fig. 4: Structural characterizations of hIAPP incubated under pH 5.5.

a Properties of hIAPP residues with +4 charges at pH 5.5: Positively charged residues in red, hydrophobic residues in blue, and residues with helical potency in the dashed box. b CD spectra of 10 μM hIAPP solution under pH 5.5 incubation at t = 0, 2, and 24 h. c Representative SERS spectra of 10 μM hIAPP solution under pH 5.5 incubation at t = 0 h (black) and t = 2 h (green). d The disulfide bond region of (c). e The Tyr doublets region of (c). f The amide I region of (c). g Secondary derivative spectra of (f). The term (arb. units) is abbreviated for arbitrary units. Representative spectra were observed more than 10 times in parallel SERS measurements. h Mapping of secondary derivative spectra of the amide I region of the SERS spectra of hIAPP at t = 2 h incubation under pH 5.5 from parallel experimental sessions. The color bar shows the normalized intensities from low (dark blue) to high (red-black). i Representative time evolution of secondary structure per residue of monomeric hIAPP with +4 charges at pH 5.5. Color legends for secondary structures: White: Coil; Green: Bend; Blue: α-Helix; Grey: 3-Helix; Yellow: Turn; Red: β-Sheet; Black: β-Bridge. j Snapshots of the initial conformation (0 ns), predominant conformation (68 ns), and final conformation (200 ns) from (i). k Statistical analysis of the secondary structural contents of the monomeric hIAPP from (i).