Central cyclic part of the hinge peptide (a parallel dimer of the pentapeptide Boc-Cys-Pro-Pro-Cys-Pro-NHCH3 with two disulfide bonds) derived from the sequence of human IgG1 is a rather rigid structure having predominantly polyproline II helical conformation as shown by vibrational circular dichroism spectra. It exhibits significant Raman optical activity (ROA) signal due to vibrations associated with the disulfide bridges. We report positive ROA for the S-S stretching vibration at 510 cm-1 and for the C-S stretching vibration at 655 cm-1. These signals can provide means to assess the conformation of disulfide bridges in proteins, otherwise difficult to investigate.
Vibrational Circular Dichroism (VCD) spectra of unblocked l‐proline oligopeptides, (Pro)n n = 3 to 7, dissolved in D2O are reported. For these oligomers, the VCD spectra can be attributed to a conformational dominance of the trans amide conformation with subunits interrelated by a left‐handed twist, particularly for the longer oligomers. As a function of oligomer length, formation of this conformation starts at n = 3; and by n = 5 a spectrum closely resembling that of the poly‐l‐proline II helix in shape and magnitude is seen. The VCD data are compared with previous (Pro)n results using IR, CD, Raman and NMR spectroscopies, and reasons for the variations in interpretation are discussed.
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