Figure 2

(A–C) EM images of fibrils formed in the presence of different ratios of the GSH-GSSG redox couple. In (A) hIAPP was incubated using 2 mM GSSG to produce a completely oxidized hIAPP. (B) hIAPP was incubated using 35 mM GSH yielding 100% hIAPP^red, whereas in (C) hIAPP was incubated in a buffer containing 0.2 mM GSSG and 4.98 mM GSH yielding 50% hIAPP^red and 50% hIAPP^ox. The scale bar denotes 200 nm. (D) ¹H,¹⁵N-HSQC spectra of the reduced (red) and oxidized (black) hIAPP in aqueous buffer (30 mM acetic acid, pH 5.3). Amino acids are labelled according to their type and sequence number. Major chemical shift changes upon disulfide bond formation are indicated by black dashed lines. The NMR chemical shifts are deposited in the BMRB (BMRB ID: 34069). (E) ¹H,¹⁵N HSQC spectra to probe the hIAPP redox state. Fibrils were prepared under the three redox conditions described in (A–C). Before the NMR experiment, fibrils were dissolved in organic solvent. (F) Model of the hIAPP aggregation mechanism. ER stress results in production of a small amount of hIAPP^red in the cell. hIAPP^red aggregates preferentially and is depleted from the pool of soluble molecules in the cell. Redox buffering continuously converts hIAPP^ox into hIAPP^red. This way, hIAPP might assist in regenerating redox equivalents under ER stress conditions.