IDENTIFICATION OF THE 150-KDA SURFACE-ANTIGEN OF ENTAMOEBA-HISTOLYTICA AS A GALACTOSE-INHIBITABLE AND N-ACETYL-D-GALACTOSAMINE-INHIBITABLE LECTIN

A monoclonal antibody that reacts with a 150-kDa protein of Entamoeba histolytica on Western immunoblotting under nonreducing conditions inh ibits the adherence and cytotoxicity of the ameba to mammalian cells i n vitro. Affinity purification of solubilized trophozoites using the m onoclonal antibody and electophoresis yielded three glycoproteins with molecular masses of 150, 170, and 260 kDa, suggesting the existence o f either a common epitope or the close association of these proteins. The 260-kDa fraction was identified as the well-known galactose (Gal)- and N-acetyl-D-galactosamine (GalNAc)-inhibitable lectin. The 150- an d 170-kDa fractions seemed to exist as part of a 380-kDa native protei n with an isoelectric point of pH 6.9. The N-terminal amino acid seque nce of the 150-kDa protein was unique, indicating that the protein was not a degraded product of the 260-kDa lectin. By gel filtration, the 260-kDa lectin and the 150/170-kDa protein could be separated. When Ch inese hamster ovary cells were pretreated with the fraction consisting of the 150/170-kDa protein the adherence of trophozoites to Chinese h amster ovary cells was competitively inhibited to a level equivalent t o that observed for the 260-kDa lectin. The inhibitory effect was lost in the presence of Gal and GalNAc but was not influenced by the prese nce of glucose. These results demonstrate that the 150/170-kDa protein is a Gal/GalNAc-inhibitable lectin. The existence of a sugar-binding domain in the protein was confirmed by Gal-affinity chromatography.