Effects of an arginine-selective tagging procedure on the fragmentation behavior of peptides studied by electrospray ionization tandem mass spectrometry (ESI-MS/MS)

The presence of arginine as the naturally occurring amino acid with the highest gas-phase basicity strongly influences the fragmentation behavior of peptides undergoing collision-induced dissociation. Using a derivatization procedure recently developed in our group, based on a reversible reaction of the guanidino group with 2,3-butanedione and an arylboronic acid, we examined how this label affects the fragmentation patterns of labeled versus unlabeled peptides in MS/MS experiments. As part of this fundamental study, two groups of model peptides (angiotensins and bradykinins) as well as tryptic peptides were labeled according to our protocol and subjected to collision-induced dissociation (CID) in both a triple quadrupole and a quadrupole ion trap instrument. It was found that for angiotensins containing an AspArg sequence, C-terminal cleavage at Asp that occurs for native peptides was completely inhibited in Arg-labeled peptides. For bradykinins and peptides obtained from tryptic digests of standard proteins, some sample peptides were little affected by the tagging of arginine residues. Others, in contrast, exhibited an almost total loss of nonspecific backbone cleavage and their fragment ion spectra were dominated by loss of the arginine tag. These and other experimental results are discussed in view of the nature of the arginine tag and the concept of proton mobility.