Substructural specificity and polyvalent carbohydrate recognition by the Entamoeba histolytica and rat hepatic N- acetylgalactosamine/galactose lectins

Both the Entamoeba histolytica lectin, a virulence factor for the causativeagent of amebiasis, and the mammalian hepatic lectin bind toN-acetylgalactosamine (GalNAc) and galactose (Gal) nonreducing termini onoligosaccharides, with preference for GalNAc. Polyvalent GalNAc-derivatized neoglycoproteins have >1000-fold enhanced binding affinityfor both lectins (Adler,P., Wood,S.J., Lee,Y.C., Lee,R.T., Petri,W.A.,Jr.and Schnaar,R.L.,1995, J. Biol. Chem ., 270, 5164-5171). Substructuralspecificity studies revealed that the 3-OH and 4-OH groups of GalNAc wererequired for binding to both lectins, whereas only the E.histolytica lectinrequired the 6-OH group. Whereas GalNAc binds with 4-fold lower affinity tothe E.histolytica lectin than to the mammalian hepatic lectin,galactosamine and N-benzoyl galactosamine bind with higher affinity to theE. histolytica lectin. Therefore, a synthetic scheme for convertingpolyamine carriers to poly-N-acyl galactosamine derivatives (linked throughthe galactosamine primary amino group) was developed to test whether suchligands would bind the E.histolytica lectin with high specificity and highaffinity. Contrary to expectations, polyvalent derivatives includingGalN6lys5, GalN4desmosine, GalN4StarburstTMdendrimer, andGalN8StarburstTMdendrimer demonstrated highly enhanced binding to themammalian hepatic lectin but little or no enhancement of binding to theE.histolytica lectin. We propose that the mammalian hepatic lectin bindswith greatest affinity to GalNAc "miniclusters," which mimic branchedtermini of N-linked oligosaccharides, whereas the E.histolytica lectinbinds most effectively to "maxiclusters," which may mimic more widelyspaced GalNAc residues on intestinal mucins.