Studies on O‐glycans of Plasmodium‐falciparum‐infected human erythrocytes Evidence for O‐GlcNAc and O‐GlcNAc‐transferase in malaria parasites

Abstract

O-Glycosylation is the major form of protein glycosylation in human erythrocytes infected with the asexual intraerythrocytic stage of the malaria parasite, Plasmodium falciparum. This study compares aspects of O-glycosylation in P. falciparum-infected and uninfected erythrocytes. Non-labeled and metabolically glucosamine-labeled O-glycans were obtained from the protein fraction of infected or uninfected erythrocytes by β elimination. Additional label was introduced by reduction with sodium borohydride, or by the attachment of radioactive Gal to peripheral GlcNAc using galactosyltransferase. 2–4-times more labeled O-glycans were obtained from infected erythrocytes compared to the same number of uninfected ones, consistent with additional biosynthesis by the parasite. Our analysis of these O-glycans showed no significant qualitative divergence between the O-glycans of the infected and those of the uninfected red cell. According to preliminary alditol analyses, the O-glycans of P. falciparum-infected red cells do not contain GalNAc at their reducing terminus. Moreover, GalNAc was not synthesized by P. falciparum from either Glc, Gal, GlcN or GalN. At least one O-glycan found in P. falciparum-infected erythrocytes contains GlcNAc at its reducing terminus. Gel-filtration results had suggested the presence of O-GlcNAc on proteins in the infected erythrocyte. Probing with a synthetic pentapeptide, we could show that P. falciparum expresses its own O-GlcNAc transferase during intracrythrocytic development. Using this peptide, the enzyme was characterized to some degree. The localization and function of O-GlcNAc in P. falciparum remains to be elucidated.