Unique fragmentation of singly charged DEST cross-linked peptides.

It has previously been shown that when cross-linking reagent diethyl suberthioimidate (DEST) reacts with primary amines of proteins to yield amidinated residues, the primary amines retain their high basicity, and cross-linked species can be enriched by strong cation exchange. It is now demonstrated that collisional activation of singly-charged DEST cross-linked peptide ions leads to preferential cleavage at the cross-linked sites. The resulting product ions facilitate the detection and identification of cross-linked peptides.