Complementary structural information from a tryptic N-linked glycopeptide via electron transfer ion/ion reactions and collision-induced dissociation

Abstract

Glycosylation is an important post-translational modification. Analysis of glycopeptides is difficult using collision-induced dissociation, as it typically yields only information about the glycan structure, without any peptide sequence information. We demonstrate here how a 3D-quadrupole ion trap, using the complementary techniques of collision induced dissociation (CID) and electron-transfer dissociation (ETD), can be used to elucidate the glycan structure and peptide sequence of the N-glycosylated peptide from a fractionated tryptic digest of the lectin from the coral tree, Erythina cristagalli. CID experiments on the multiply protonated glycopeptide ions yield, almost exclusively, cleavage at glycosidic bonds, with little peptide backbone fragmentation. ETD reactions of the triply charged glycopeptide cations with either sulfur dioxide or nitrobenzene anions yield cleavage of the peptide backbone with no loss of the glycan structure. These results show that a 3D-quadrupole ion trap can be used to provide glycopeptide amino acid sequence information as well as information about the glycan structure.

Figure 1

Collision-induced dissociation spectrum of a) the [M+3H]³⁺ glycopeptide ion, and b) the [M+2H]²⁺ glycopeptide ion formed by ion/ion proton-transfer reactions with PDCH.

Figure 2

Electron-transfer dissociation spectrum of a) the [M+3H]³⁺ glycopeptide ion after reaction with sulfur dioxide anions, and b) the [M+3H]³⁺ glycopeptide ion after reaction with nitrobenzene anions. Ions corresponding to fragmentation of the glycan structure likely arises from CID of the [M+3H]³⁺ and [M+2H]²⁺ ions during mass analysis, as described in the text.