UV photofragmentation dynamics of protonated cystine: disulfide bond rupture

International audienceDisulfide bonds (S−S) play a central role in stabilizing the native 9 structure of proteins against denaturation. Experimentally, identification of these linkages in peptide and protein structure characterization remains challenging. UV photodissociation (UVPD) can be a valuable tool in identifying disulfide linkages. Here, the S−S bond acts as a UV chromophore and absorption of one UV photon corresponds to a σ−σ* transition. We have investigated the photodissociation dynamics of protonated cystine, which is a dimer of two cysteines linked by a disulfide bridge, at 263 nm (4.7 eV) using a multicoincidence technique in which fragments coming from the same fragmentation event are detected. Two types of bond cleavages are observed corresponding to the disulfide (S−S) and adjacent C−S bond ruptures. We show that the S−S cleavage leads to three different fragmentions via three different fragmentation mechanisms. The UVPD results are compared to collision-induced dissociation (CID) and electron-induced dissociation (EID) studies