Direct elucidation of disulfide bond partners using ultraviolet photodissociation mass spectrometry.

Disulfide bonds stabilize the tertiary and quaternary structure of proteins. Identifying the correct disulfide bond pairs can be extremely useful to understand the nature of a protein. However identifying correct disulfide linkages remains a challenge for many proteins. We report the use of ultraviolet photodissociation (UVPD) at 266 nm to selectively cleave disulfide bonds in the gas phase, while leaving all other bonds intact. This methodology can be used to identify disulfide bonded pairs in complex systems with multiple disulfide bond partners. We have explored UVPD chemistry on pairs of model peptides with one disulfide bond to evaluate the importance of various sequence and structural effects. In addition, online experiments were performed on whole protein digests. Bond selective UVPD was able to correctly identify and characterize all known disulfide bonded pairs. The method also proved sufficiently sensitive to identify and characterize several non-native disulfide-bound peptide pairs which were present in trace amounts. Photodissociation at 266 nm can be a valuable tool for disulfide bond identification and pair assignment in high-throughput proteomics studies.