Disulfide linkage Raman markers: A reconsideration attempt

During the last decades, Raman spectroscopy has been routinely used for probing the conformational features of disulfide linkages in peptides and proteins. However, the interpretation of disulfide Raman markers is currently performed by a simple rule derived from the earliest observations on dialkyl disulfides. More precisely, this rule consists of the following: (1) in analyzing the Raman bands in the 550-500 cm-1 region ascribed to disulfide bond stretch motion, namely, ν(S-S), and (2) assigning the three types of Raman markers observed at ~500, ~520, and ~540 cm-1 to three families of rotamers defined along the three successive bonds of the -C-S-S-C- moiety, referred to as ggg, ggt, and tgt. In this report, we attempt to show that an accurate analysis of disulfide vibrational features needs the use of the five torsion angles (χ1, χ2, χ3, χ2', and χ1') along the five successive bonds joining the two α-carbon atoms in the cystine (Cys-Cys) unit. The present work is inspired by the disulfide conformational investigations performed by a statistical scan of numerous protein crystal and nuclear magnetic resonance data, taking into account the handedness (right and left) of a disulfide bridge, its spatial shape (Staple, Hook, and Spiral), as well as the signs of the two extreme torsion angles χ1 and χ1'. It appears that the combined use of the old and recent conformational notations allows a more accurate structural and vibrational analysis of disulfide linkage. Copyright © 2014 John Wiley & Sons, Ltd. It has been shown that the old notations (ggg, ggt, and tgt) are insufficient for analyzing the conformational and vibrational features of disulfide linkages in peptides and proteins. This failure can be improved by considering the new topological notations based on the signs of the five torsion angles in going from one α-carbon to the other in the cystine unit. Copyright © 2014 John Wiley & Sons, Ltd.This work was granted access to the HPC resources of CINES (Montpellier, France) under the allocations c2013075065 and c2014085065 made by GENCI (Grand Equipement National de Calcul Intensif). The authors would like to acknowledge CSIC for the Project I-LINK 0646 facilitating the collaboration between the Spanish and French groups.Peer Reviewe