Glycobiology of MSP-1 and MSP-2: Potential malaria vaccine candidate glycoproteins

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-PA GE of the labelled material provided effective labelling of the MSP-1 195 k De, and MSP-2, 42-53 kDa, glycoproteins. Reductive beta-elimination of the MSP-2 released from the gel consisted of glycopeptides containing labelled sugars. Processing of the eliminated components and identification of the s ugar residues demonstrated the presence of N-acetylglucosaminitol and N-ace tylgalactosaminitol amongst other labelled sugars Reductive beta-eliminatio n with soduim hydroxide-sodium borotritideborohydride showed the presence o f glucosaminitol and alanine in the hydrolysis products. The MSP-2 was reta ined on solid phase wheat-germ agglutinin and was released from the lectin by treatment with GlcNAc. Upon treatment with O-glycanase the MSP-2 glycopr otein released labelled amino sugar, and derived oligosaccharides on treatm ent with exoglycosidases released labelled components corresponding to the metabolically incorporated sugars. Labelled Gal was incorporated into the M SP-2 glycoprotin using [H-3]UDP-Gal and galactosyltransferase. The galacosy lated glycoprotein released labelled Gal upon treatment with beta-galactosi dase. 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-glycosyl linkage and the glycoprotein has terminal GlcNAc and Gal residues. The carbohydrate moieties of MSP-2. glyc oprotein consist mainly of short chains linked to the protein core. Mannosa mine inhibits biosynthesis as well as parasitemia of P.facliparum.