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Carbohydrate moeity of Plasmodium falciparum glycoproteins: The nature of the carbohydrate‐peptide linkage in the MSP‐2 glycoprotein

Metabolic labelling of Plasmodium falciparum parasites with [3H]GIcN, [3H]Man, [3H]Gal and [3H]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 β‐elimination of the MSP‐2 released from the gel consisted of glycopeptides containing labelled sugars. Processing of the eliminated components and identification of the sugar residues demonstrated the presence of N‐acetylglucosaminitol and N‐acetylgalactosaminitol amongst other labelled sugars. Reductive β‐elimination with sodium hydroxide‐sodium borotritide‐borohydride showed the presence of glucosaminitol and alanine in the hydrolysis products. The MSP‐2 was retained on solid phase wheat‐germ agglutinin and was released from the lectin by treatment with GIcNAc. Upon treatment with O‐glycanase the MSP‐2 glycoprotein released lablled amino sugar, and derived oligosaccharides on treatment with exoglycosidases released labelled components corresponding to the metabolically incorporated sugars. Labelled Gal was incorporated into the MSP‐2 glycoprotein using [3H]UDP‐Gal and galactosyltransferase. The galactosylated glycoprotein released labelled Gal upon treatment with β‐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‐sedne/threonine in O‐glycosyl linkage and the glycoprotein has terminal GlcNAc and Gal residues. The carbohydrate moieties of MSP‐2, glycoprotein consist mainly of short chains linked to the protein core.