GLYCOSYLPHOSPHATIDYLINOSITOL ANCHORS REPRESENT THE MAJOR CARBOHYDRATEMODIFICATION IN PROTEINS OF INTRAERYTHROCYTIC STAGE PLASMODIUM-FALCIPARUM

The nature and extent of carbohydrate modification in intraerythrocyti c stage Plasmodium falciparum proteins have been controversial. This s tudy describes the characterization of the carbohydrates in intraeryth rocytic P. falciparum proteins and provides an overall picture of the nature of carbohydrate modification in the parasite proteins. P. falci parum strains were metabolically labeled with radioactive sugar precur sors and ethanolamine at different developmental stages. The individua l parasite proteins separated on SDS-polyacrylamide gels and whole par asite cell lysates were analyzed for the carbohydrate moieties. The re sults established the following: 1) glycosylphosphatidylinositol (GPI) anchors represent the major carbohydrate modification in the intraery throcytic stage P. falciparum proteins; 2) in contrast to previous rep orts, O-linked carbohydrates are either absent or present only at very low levels in the parasite; and 3) P. falciparum contains low levels of N-glycosylation capability. The amount of N-linked carbohydrates in whole parasite proteins is approximately 6% compared with the GPI anc hors attached to proteins based on radioactive GlcN incorporated into the proteins. The glycan cores of multiple parasite protein GPI anchor s are all similar, consisting of -1-2)6Man-alpha-1-2Man-alpha-1-6Man-a lpha-1-4GlcN. The fourth Man residues distal to GlcN of the GPI anchor glycan cores contain unidentified substituents that are susceptible t o conditions of nitrous acid deamination. This unusual structural feat ure may contribute to the reported pathogenic properties of the P. fal ciparum GPI anchors.