Synthesis and preliminary evaluation of neoglycopolymers carrying multivalent N-glycopeptide units

In the present study, for the discovery of uncharacterized glycan-binding receptors or lectin-like receptors in plants, we developed neoglycopolymers to which three types of N-glycopeptides are conjugated; the first with plant complex type N-glycan (M3FX), the second with high-mannose type N-glycan (M8), and the third with animal complex type N-glycan (NeuAc2Gal2GN2M3). Three types of Asn-oligosaccharide (Asn-M3FX, Asn-M8, or Asn-NeuAc2Gal2GN2M3) were prepared from storage glycoproteins of Ginkgo biloba seeds, Vigna angularis seeds, and egg yolk glycopeptides from actinase digests of each glycoproteins or glycopeptide. Neoglycopolymers were synthesized such that the α-amino groups of Asn-oligosaccharide were coupled to the carboxyl groups of poly-γ-L-glutamic acid (γ-L-PGA) with 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride n-hydrate (DMT-MM). The resulting neoglycopolymers were purified through a combination of gel-filtration and reverse-phase HPLC. The incorporation of N-glycans into γ-L-PGA (mol%) was estimated through amino acid composition analysis after acid hydrolysis. The incorporation rates of Asn-M3FX, Asn-M8, and Asn-NeuAc2Gal2GN2M3 into γ-L-PGA were 15.4%, 8.6%, and 11.1%, indicating that nearly 890, 500, and 640 molecules of N-glycans were conjugated with γ-L-PGA, respectively. Furthermore, we confirmed that the neoglycopolymer carrying the multivalent high-mannose type N-glycans is a useful tool for rapid purification of mannose-binding protein, Concanavalin A, from jack bean extract.