CARBOHYDRATE MOIETY OF PLASMODIUM-FALCIPARUM GLYCOPROTEINS - THE NATURE OF THE CARBOHYDRATE-PEPTIDE LINKAGE IN THE MSP-2 GLYCOPROTEIN

Metabolic labelling of Plasmodium falciparum parasites with [H-3]GlcN, [H-3]Man, [H-3]Gal and [H-3]ethanolamine, and subsequent purification by SDS-PAGE of the labelled material provided effective labelling of the MSP-1, 195 kDa, and MSP-2, 42-53 kDa, glycoproteins. Reductive bet a-elimination of the MSP-2 released from the gel consisted of glycopep tides containing labelled sugars. Processing of the eliminated compone nts and identification of the sugar residues demonstrated the presence of N-acetylglucosaminitol and N-acetylgalactosaminitol amongst other labelled sugars. Reductive beta-elimination with sodium hydroxide-sodi um borotritide-borohydride showed the presence of glucosaminitol and a lanine in the hydrolysis products. The MSP-2 was retained on solid pha se wheat-germ agglutinin and was released from the lectin by treatment with GlcNAc. Upon treatment with O-glycanase the MSP-2 glycoprotein r eleased lablled amino sugar, and derived oligosaccharides on treatment with exoglycosidases released labelled components corresponding to th e metabolically incorporated sugars. Labelled Gal was incorporated int o the MSP-2 glycoprotein using [H-3]UDP-Gal and galactosyltransferase. The galactosylated glycoprotein released labelled Gal upon treatment with beta-galactosidase. The results of the present study suggest that the carbohydrate chains of the MSP-2 glycoprotein are attached to the protein backbone via GlcNAc- and GalNAc-serine/threonine in O-glycosy l linkage and the glycoprotein has terminal GlcNAc and Gal residues. T he carbohydrate moieties of MSP-2, glycoprotein consist mainly of shor t chains linked to the protein core.