A Bacterial Mannose Binding Lectin as a Tool for the Enrichment of C-and O- Mannosylated Peptides

C-mannosylated peptides are easily detected by mass spectrometry (MS) from purified proteins but not from complex biological samples. Enrichment of specific glycopeptides by lectin affinity prior to MS analysis has been widely applied to support glycopeptide identification, but was up till now not available for C-mannosylated peptides. Here we used the α-mannose-specific Burkholderia cenocepacia lectin A (BC2L-A) and show that, in addition to its previously demonstrated high-mannose N-glycan binding capability, this lectin is able to retain C- and O-mannosylated peptides. Next to testing binding abilities to standard peptides, we applied BC2L-A affinity to enrich C-mannosylated peptides from complex samples of tryptic digests of HEK293 and MCF10A whole cell extracts, which led to the identification of novel C-mannosylation sites. In conclusion, BC2L-A enabled specific enrichment of C- and O-mannosylated peptides and might have superior properties over other lectins for binding to α-mannose-terminating glycans.