Raman optical activity of the hinge peptide

We report results of Raman optical activity investigation of the hinge peptide (a parallel dimer of the octapeptide H-Thr-Cys-Pro-Pro-Cys-Pro-Ala-Pro-OH with two disulphide bonds) derived from the sequence of human IgG1, its single thread model (a linear octapeptide H-Thr-Met-Pro-Pro-Met-Pro-Ala-Pro-OH), S-S bridged tetrapeptide (H-Gly-Cys-OH)2 and poly-l-proline. The ROA spectra confirm PPII as a prevailing conformation of the double thread hinge peptide in aqueous solution while for its single thread Met analog PPII conformation as the only conformation. Diagnostic positive ROA band at 1320 cm−1 remains present even in proline-rich peptides and can serve as reliable PPII marker. Significant positive ROA signal related to C-S stretching vibration has been found but a clear ROA signature of S-S stretching mode still remains uncertain.