Entamoeba histolytica trophozoites initiate pathogenic colonization by adherence to host glycoconjugates via an amebic surface lectin which binds to galactose (Gal) and N-acetylgalactosamine (GalNAc) residues. Monovalent and multivalent carbohydrate ligands were screened for inhibition of E. histolytica lectin-mediated human red cell hemagglutination, revealing that: (i) the synthetic multivalent neoglycoprotein GalNAcBSA (having an average of 39 GalNAc residues linked to bovine serum albumin) was 140,000-fold more potent an inhibitor than monovalent GalNAc and 500,000-fold more potent than monovalent Gal; and (ii) small synthetic multivalent ligands which bind with high affinity to the mammalian hepatic Gal/GalNAc lectin do not bind with high affinity to the E. histolytica lectin. Radioligand binding studies revealed saturable binding of I-GalNAcBSA to E. histolytica membranes (K = 10 ± 3 nM, B = 0.9 ± 0.08 pmol/mg membrane protein). Maximal binding required the presence of calcium chloride (300 µM) or sodium chloride (50 mM), and had a broad pH maximum (pH 6-9). GalNAcBSA was 200,000-fold more potent than monovalent GalNAc in blocking radioligand binding. Among synthetic saccharide-derivatized linear polymers, the GalNAc and GalNAc3Gal derivatives were the most potent, with GalNAc and GalNAc3(Fuc2)Gal derivatives much weaker. The data support a model in which a unique pattern of spaced multiple GalNAc residues are the highest affinity targets for the E. histolytica lectin.

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