New Peptide Dissociation Method For Mass Spec

Analysis of peptides in proteomics experiments requires the use of dissociation methods that break the peptides into smaller pieces to determine the amino acid sequence. Gavin E. Reid and coworkers of Michigan State University describe a new dissociation method, called femtosecond laser-induced ionization/dissociation (fs-LID), that overcomes some of the limitations of other dissociation methods (J. Am. Chem. Soc., DOI: 10.1021/ja8089119). In fs-LID, ultrashort laser pulses (<35 femtosecond) deposit sufficient energy into the peptides to cause them to dissociate. The researchers demonstrated fs-LID of the singly and multiply protonated ions of angiotensin II, Glu-fibrinopeptide B, and several phosphorylated peptides. In each case, fs-LID provided equivalent or better sequence ion coverage, including the less common c-, x-, and z-type product ions, compared with collision-induced dissociation (CID). A particular advantage of fs-LID is in the sequence analysis and characterization of peptides containing posttranslational modifications such as phosphorylation; CID commonly results in extensive loss of the phosphate side chain or the observation of rearrangement reactions that can severely limit the ability to correctly identify the site of phosphorylation.