N-glycan analysis of mannose/glucose specific lectin from Dolichos lablab seeds

• Mannose/glucose specific lectin was affinity purified from lablab bean.
• PMF showed identity with FRIL composed of four α subunits and one β subunit.
• N-glycopeptides were enriched from in-gel digestion of α subunits by ZIC-HILIC.
• α 2–4 subunits were found to contain paucimannose type N-glycan.
• Differential glycosylation was observed in α subunits.

An affinity purified mannose/glucose specific lectin from the seeds of Dolichos lablab (Indian bean/lablab bean) resolves into five subunits upon SDS-PAGE in the range of Mr 12–20 kDa. Partial de novo sequencing of subunits resulted in 88% and 73% sequence coverage for α and β subunits of the cDNA derived FRIL (Flt3 receptor interacting lectin) sequence, respectively and suggested that four bands correspond to the α-subunits while the band of lowest molecular mass is designated as β. It was proposed in an earlier study on FRIL that the difference in molecular mass of α-subunits is due to differences in C-terminal processing and differential N-glycosylation i.e. numbers of N-glycans present (Colucci et al., 1999). Thus, differential N-glycosylation of the purified mannose/glucose specific lectin was unravelled by in-gel trypsin/chymotrypsin digestion of the α-subunits followed by desalting and ZIC-HILIC enrichment of N-glycopeptides. Subsequently, analyses by nano electrospray ionisation quadrupole time of flight mass spectrometry and low-energy collision-induced dissociation experiments revealed the presence of a typical paucimannose type N-glycan (Man2(Xyl)GlcNAc2(Fuc)) in α subunits 2–4.