The CD spectrum (Fig. )) shows one pronounced minimum at 199 nm with intensities around -10 deg cm 2 dmol -1 . This spectral signature, albeit usually with an stronger intensity, is well-known for disordered conformations in peptides and proteins. Analysis of the secondary structure elements via BeStSel 25 reveals contributions of about 25 % of 'anti-parallel β-sheet', 20 % of 'turn', and more than 50 % of 'other' elements, which is an indication of a predominantly, but not completely disordered conformational ensemble. The broad amide I band in the IR spectrum between 1600-1700 cm -1 (Fig. ) and in the Raman spectrum at 1684 cm -1 57 (Fig. ) are supportive of a mostly disordered peptide structure. The maximum at 1673 cm -1 could indicate β-turn or β-sheet structure in the peptide's ensemble, while the shoulder around 1642 cm -1 is assigned to disordered structures. The peptide's side chains, such as histidine, lysine, asparagine and glutamine, contribute to the overall amide I' shape, as well as the shoulder around 1590 cm -1 . IR contributions in the lower amide I' region (1600-1650 cm -1 ) stem from intra-molecular hydrogen bonding in turns and helical elements, C=O(NH 2 ) stretching (around 1650 cm -1 ), COO -asymmetric stretching (1580-1600 cm -1 ), NH + 3 deformations (around 1620 cm -1 ), different protonation states of the His residues, and hydrogen bonding to the solvent. A minor degree of order in our peptide may be inferred from the shape of the amide I' IR peak, consistent with the CD result. The amide II region arises from C-N stretching coupled with For this reason, while the amide II is also conformationally sensitive, it is less commonly used for conformational analysis. In the ROA spectrum (Fig. )), a broad positive signal is observed at 1677 cm -1 , which is also typical for mostly disordered peptides, whereas α-helical or β-sheet structures would display a -/+ couplet in this region. The amide III region in the Raman and ROA spectra (1240 to 1310 cm -1 ) arises from complex vibrational modes with out-of-phase N-H bending vibrations coupled with the amide C α -H bond stretching mode. The coupling of these vibrations with C α -H bending modes makes this spectral region very sensitive to the precise backbone conformation. The positive band at 1318 cm -1 in the ROA spectrum is typically observed for disordered peptides and proteins, mainly arising from the backbone's torsional angles clustering in the Ramachandran region of the left-handed polyproline II (PPII) helix (ϕ ∼ 75 • and ψ ∼ 145 • ). A more detailed interpretation requires molecular-level information about the conformer population of the peptide, which we can predict from all-atom MD simulations, as described in the next section.