Plasmodium falciparum Pf34, a novel GPI-anchored rhoptry protein found in detergent-resistant microdomains

Apicomplexan parasites are characterised by the presence of specialised organelles, such as rhoptries, located at the apical end of invasive forms that play an important role in invasion of the host cell and formation of the parasitophorous vacuole. In this study, we have characterised a novel Plasmodium falciparum rhoptry protein, Pf34, encoded by a single exon gene located on chromosome 4 and expressed as a 34 kDa protein in mature asexual stage parasites. Pf34 is expressed later in the life cycle than the previously described rhoptry protein, Rhoptry Associated Membrane Antigen (RAMA). Orthologues of Pf34 are present in other Plasmodium species and a potential orthologue has also been identified in Toxoplasma gondii. Indirect immunofluorescence assays show that Pf34 is located at the merozoite apex and localises to the rhoptry neck. Pf34, previously demonstrated to be glycosyl-phosphatidyl-inositol (GPI)-anchored [Gilson, P.R., Nebl, T., Vukcevic, D., Moritz, R.L., Sargeant, T., Speed, T.P., Schofield, L., Crabb, B.S. (2006) Identification and stoichiometry of GPI-anchored membrane proteins of the human malaria parasite Plasmodium falciparum. Mol. Cell. Proteomics 5, 1286-1299.], is associated with parasite-derived detergent-resistant microdomains (DRMs). Pf34 is carried into the newly invaded ring, consistent with a role for Pf34 in the formation of the parasitophorous vacuole. Pf34 is exposed to the human immune system during infection and is recognised by human immune sera collected from residents of malaria endemic areas of Vietnam and Papua New Guinea.