Entamoeba histolytica: Deletion of the GPI anchor signal sequence on the Gal/GalNAc lectin light subunit prevents its assembly into the lectin heterodimer

Adherence and cytotoxicity of Entamoeba histolytica require the function of a heterodimeric galactose and N-acetylgalactosamine (Gal/GalNAc)-specific lectin. The lectin heavy subunit (Hgl) contains a carbohydrate recognition domain and mediates inside-out cell signaling via its cytoplasmic tail. The function of the lectin light subunit (Lgl) is unknown. The lectin has a un ique mechanism of membrane association: Hgl is transmembrane but Lgl is gly cosylphosphatidylinositol (GPI) anchored. The role of the CPI anchor signal sequence in heterodimer assembly was tested. Epitope-tagged Lgl with or wi thout the GPI anchor addition signal was expressed in E. histolytica tropho zoites. Tagged Lgl did not assemble with Hgl into a lectin heterodimer in t he absence of the GPI addition signal. Consistent with previous results tha t only the Hgl subunit mediates adherence, the monomeric Lgl without the GP I anchor signal lacked Gal/GalNAc-binding activity, (C) 2000 Academic Press .