REMOVAL OF SIALIC-ACID FROM MUCIN-LIKE SURFACE MOLECULES OF TRYPANOSOMA-CRUZI METACYCLIC TRYPOMASTIGOTES ENHANCES PARASITE-HOST CELL-INTERACTION

The 35/50 kDa mucin-like surface glycoprotein (gp 35/50) of Trypanosom a cruzi metacycliic trypomastigotes has been in mammalian cell invasio n. In this study we investigated whether the sialyl residues of gp35/5 0 are required for interaction of parasites with target cells. After t reatment with bacterial neuraminidase, the metacyclic forms (G strain) remained reactive with the monoclonal antibody (mAb) 10D8 but lost th eir reactivity with mAb 3C9, that recognizes sialic acid-containing ep itopes on gp35/50, and entered HeLa cells in significantly higher numb ers as compared to untreated controls. Resialylation of gp35/50, by in cubation of parasites with T. cruzi trans-sialidase and sialyl lactose , restored the reactivity with mAb 3C9 as well as the affinity for sia lic acid specific lectin. Accordingly, the rate of invasion of resialy lated parasites was reduced to levels similar to those observed before desialylation. Purified G strain gp35/50, desialylated by neuraminida se treatment, bound to HeLa cells more than its sialylated counterpart . The Ca2+ signaling activity, which has been associated with cell inv asion, was also determined by measuring the cytosolic Ca2+ concentrati on ([Ca2+](i)), in HeLa cells upon interaction with sonicated extracts from untreated or neuraminidase-treated parasites, or with purified g p35/50 in its sialylated or desialylated form. Consistent with the res ults of cell invasion assay, the desialylated parasite preparations, a s well as the sialic acid free gp35/50, induced an average elevation i n [Ca2+](i) significantly higher than that triggered by untreated cont rols. None of these effects, namely the increase in infectivity and Ca 2+ signaling activity, was observed with neuraminidase-treated CL stra in metacyclic trypomastigotes, which express a variant form of sialic acid gp35/50 molecule that is not recognized by mAb 10D8 and apparentl y is not involved in target cell invasion. Copyright (C) 1997 Elsevier Science B.V.