THE DEVELOPMENTALLY-REGULATED TRANS-SIALIDASE FROM TRYPANOSOMA-BRUCEISIALYLATES THE PROCYCLIC ACIDIC REPETITIVE PROTEIN

A developmentally regulated trans-sialidase activity is present on the surface of procyclic Trypanosoma brucei. Bloodstream stages display n o trans-sialidase activity. T. brucei trans-sialidase is capable of tr ansferring sialic acids from a variety of glycoconjugates into new gly cosidic linkages without requirement for CMP-Neu5Ac. The enzyme is lin ked to the plasma-membrane via a GPI-PLC-resistant GPI-anchor. The com parison of enzymic and structural features of sialidase and trans-sial idase suggests that the two activities may be catalyzed by the same pr otein, since highly enriched sialidase fractions display trans-sialida se activity. 2-Deoxy-2,3-didehydro-N-acetylneuraminic acid is only a p oor inhibitor for the two enzymic activities. Sialic acids are transfe rred to alpha(2-3)-positions of terminal beta-galactose residues of ol igosaccharides and glycoconjugates at various rates. Neu5Ac-alpha(2-3) -lactose is the best trans-sialylation donor tested. Lewis(x) is a poo r sialic acid acceptor. T. brucei trans-sialidase utilizes serum glyco conjugates, human and bovine erythrocytes as sialic acid donors, and r esialylates sialidase-treated erythrocytes. The enzyme transfers siali c acids from the GPI-anchor of procyclic acidic repetitive protein (PA RP) onto lactose and vice versa. Also structures within a variant surf ace glycoprotein (sVSG MITat. 1.7.) can be trans-sialylated.