Enrichment and identification of bacterial glycopeptides by mass spectrometry

Large-scale analysis of protein N- and O-linked glycosylation by mass spectrometry has traditionally been performed in eukaryotes by parallel approaches aimed at elucidating glycan structures (glycomics) and their formerly glycosylated peptides (glycoproteomics) without reference to their intact state. Such analyses depend heavily on commercial glycosidases (e.g. protein N-glycosidase F) that can remove glycans from the peptide backbone for separate analyses. Bacterial glycosylation has only recently been identified as a widespread phenomenon. In many cases however, unique bacterial sugars preclude enzymatic removal, therefore ultimately requiring a site-specific approach for intact glycopeptide analysis. Here, we describe protocols for the enrichment of bacterial glycopeptides using zwitterionic-hydrophilic interaction liquid chromatography (ZIC-HILIC) and their analysis using liquid chromatography coupled to electrospray ionization tandem mass spectrometry (LC-MS/MS) with collision-induced dissociation (CID) and higher energy collisional dissociation (HCD) fragmentation for glycan structure elucidation and glycopeptide identification.