Extended Data Fig. 5: The deconvolution of IR spectra of R300K in the range of the peptide bond vibrations.

The dots show the experimental spectrum, the individual Gaussian peaks used for the fit are displayed with thin lines of individual colors, and the cumulative fits are shown by bolder red lines. To demonstrate that there are several possibilities to fit the IR spectrum of R300K, we are providing several alternative deconvolutions of the experimental spectrum. The fitting was performed using Origin software without fixation of any band parameter. Both band positions and widths were optimized to get the closest match to the experimental spectrum. The peptide II band’s position varies depending on whether the absorption peak marked as NH₂ (1592 or 1604 cm⁻¹) is included in the fit. Our calculations predict the presence of a notably intense NH₂ scissor vibration band between peptide I and peptide II bands in the spectra of short peptides terminated by amino groups on both sides. Moreover, the match between the experimental spectrum and the fit is much better when the NH₂ absorption band is included. Therefore, the deconvolution shown in lower frames seems to be more accurate.