Peptide Mimetics of Terminal Sugars of Complex Glycans

Abstract

In this project we asked whether short peptides would mimic complex carbohydrate structures and express biological activity. Amino acid sequences were identified as potential glycan mimetics by molecular modeling of docking to binding sites of lectins. The sequence HPSLK was synthesized as a quadravalent structure from a tri-lysine scaffold. Solid-phase assays showed that this peptide bound strongly to lectins from Triticus vulgaris (wheat germ agglutinin, WGA) and Dolichos biflorus (DB), which bind monosaccharides, and to lectins from Sambucus nigra (SNA1) and Maackia amurensis (MAA), which are specific for oligosaccha- rides with terminal 5-acetylneuraminic acid-galactose sequences. Further modeling led to synthesis of a longer peptide, NPSHPSLG, along with a variant, NPSHPLSG, as quadravalent structures. The longer peptides bound weakly, if at all, to WGA and DB but bound strongly to SNA1 and MAA. Mucin inhibited binding of HPSLK to WGA and DB, while fetuin inhibited binding of NPSHPSLG and NPSHPLSG to SNA1 and MAA. These results suggest that the peptides interact with the lectins at glycan-binding sites. When tested for biological activity, the peptides stimulated internalization of opsonized microspheres, which was blocked by wortmannin, an inhibitor of phagocytosis. Whereas HPSLK stimulated phosphorylation of the signaling proteins STAT2 and STAT6, NPSHPSLG and NPSHPLSG stimulated phosphorylation of STAT6, a marker for the alternative activation of phagocytosis, more strongly than STAT2. Our results suggest that these synthetic peptides may be useful as biological response modifiers.