Intermediate subunit of the Gal/GalNAc lectin of Entamoeba histolytica is a member of a gene family containing multiple CXXC sequence motifs

Killing by Entamoeba histolytica requires parasite adherence to host galact ose- and N-acetyl-D-galactosamine (Gal/GaINAc)-containing cell surface rece ptors. A 260-kDa heterodimeric E. histolytica Gal/GaINAc lectin composed of heavy (Hgl) and light (Lgl) subunits has been previously described. Here w e present the cloning and characterization of Igl, a 150-kDa intermediate s ubunit of the Gal/GaINAc lectin. Igl, Hgl, and Lgl colocalized on the surfa ce membrane of trophozoites. Two unlinked copies of genes encoding Igl shar ed 81% amino acid sequence identity (GenBank accession no. AF337950 and AF3 37951). They encoded cysteine-rich proteins with amino- and carboxy-termina l hydrophobic signal sequences characteristic of glycosylphosphatidylinosit ol (GPI)-anchored membrane proteins. The igl genes lacked carbohydrate reco gnition domains but were members of a large family of amebic genes containi ng CXXC and CXC motifs. These data indicate that Igl is part of the parasit e's multimolecular Gal/GaINAc adhesin required for host interaction.