Purification and characterization of a 50 kDa glycoprotein in cercariae of Schistosoma mansoni

Abstract

Glycoproteins of S. mansoni were purified using concanavalin A affinity chromatography. A dominant 50 kDa glycoprotein (gp5O) was found to be unique to ConA-purified cercarial antigens (ConA-Cer), but absent in ConA-SEA or ConA-SWAP. Antigenicity study using infected mouse sera showed that gp5O not only reacted with 8-and 16-week infected mousesera, butalso with prepatent 4-week serum. Furthermore.. theN-linked oligosaccharides are required for the recognition of gp5O by infected mouse sera. Two dimensional electrophoresis (2-D) and 2-D western analyses revealed that gp5O is a single protein with an isoelectric point (pl) of 8. Studies on the nature of gp5O glycosylation demonstrated that the carbohydrates of gp5O belong to complex type N-linked glycosylation with many accessible sugars: mannose and/or glucose; GIcNAc and/or sialic acid; galactose and/or GaINAc. One of the interesting results is that gp5O is the only protein in ConA-Cer which can be recognized by Ricinus communes lectins. Using confocal laser scanning microscopy, gp5O was localized to the penetration glands of the cercarial body, indicating that it may function during the penetration. Investigations on the expression of gp5O within different life cycle stages showed that gp5O polyclonal antibody (PAb) reacted with a 60 kDa protein in adult worms, but did not react with eggs. On the other hand, gp5O PAb showed cross-reactivity with other trematode parasites, including S. haematobium and F. hepatica, but not S. japonicum. Finally, gp5O was tested as a diagnostic marker using prepatent and patent human patient sera. Because of the unique properties of gp5O and its strong reaction with prepatent human sera, we discuss its use as a potential prepatent immunodiagnostic reagent towards schistomiasis and as a vaccine candidate.