N-acetylglucosamine-binding proteins on Plasmodium falciparum merozoite surface

Plasmodium falciparum merozoite surface is specifically labelled with a neoglycoprotein bearing N-acetylglucosamine (GlcNAc) residues in a sugar-dependent manner, as shown by affinity cytochemistry in fluorescence and electron microscopy. To ascertain the nature of the sugar receptor, merozoite proteins were blotted and tested by a two-step method using biotinylated GlcNAc-bovine serum albumin (BSA) and streptavidin-peroxidase conjugate. Three parasite proteins were specifically revealed and designated as Pf 120, Pf 83 and Pf 45 GlcNAc-binding proteins. These proteins bind to a gel substituted with GlcNAc and are specifically eluted with 300 mM GlcNAc. Using a rabbit antiserum raised against Pf 83, the Pf 120 GlcNAc-binding protein, in addition to Pf 83, was labelled by Western blotting. Comparative analyses with an antibody against the Pf 83 MSP derived from the P. falciparum merozoite surface protein (Pf MSP) indicated that the Pf 83 GlcNAc-binding protein is not related to the fragment of the Pf MSP antigen. Similarly, the Pf 83 GlcNAc-binding protein is not related to the apical membrane antigen 1 (AMA 1) which also has the same molecular mass. Therefore the Pf 120, Pf 83 and Pf 45 GlcNAc-binding proteins which are located on the merozoite surface and recognize GlcNAc residues could be involved in the binding of merozoites to the glycoconjugates of the surface of the red blood cells.