Fig. 2: Orthologous techniques used to characterize the amyloid-like fibril formation of the APRs. | Nature Communications

Fig. 2: Orthologous techniques used to characterize the amyloid-like fibril formation of the APRs.

From: Polymorphic amyloid nanostructures of hormone peptides involved in glucose homeostasis display reversible amyloid formation

Fig. 2

a Characteristic circular dichroism (CD) spectra detected during the amyloid formation of glucagon-like APRs. (Supplementary Figs. 3–9 shows all CD spectra in detail.) U: U-type CD-spectrum with a negative maximum at ~200 nm characteristic to the unfolded state. β: Exendin-like sequences gave a typical B-type CD-spectrum, characteristic for β-strands (a large positive maximum at ~205 nm, with a smaller (optional) negative maximum at ~225 nm). β’: Unconventional B-type CD spectrum characterizing the glucagon-like sequences, where the intensive negative maximum at either 205–210 or 220–225 nm, is followed by a positive maximum above 225–230 nm. b FTIR spectra of APRGLP2 shortly after setting the pH neutral (red) to acidic (blue) reveals an enhanced signal in the amide I band region, characteristic of the stacked β-sheets of amyloid-like fibrils. This vibration immediately diminishes when setting the pH back to neutral (top FTIR spectrum - rev. refers to reversibility). c The ThT fluorescence measurement of APRex4 shows an almost thirtyfold increase in intensity in the case of the acidic sample (blue) compared to the neutral sample (red), which can be considered ThT-negative. The darker lines represent the averages, while the brighter belts indicate the standard deviations of three parallel measurements. d Overview of the detected signals in relation to the presence of amyloid fibrils. CD spectral shifts indicate secondary structure changes of the hexapeptides as a function of the net charge. The values in the ThT columns show the measured intensity increase ratio compared to the blank ThT sample, which is considered as 1. AFM images provide morphological insight into the assembled fibrillar nanostructures of (e) APRgluc (pH ≈ 4), (f) APRGIP (pH ≈ 4), and (g) APRTc5b (pH ≈ 7) after 24 h of agitation. Note, the same matured amyloid samples were used for FTIR and AFM measurements. Supplementary Figs. 10–15 collect all the results for each APR individually.

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