The most severe forms of human malaria are caused by Plasmodium falciparum, an apicomplexan
parasite that undergoes asexual replication within red blood cells. Infected erythrocytes
gain the ability to adhere to endothelial cells in the host microvasculature
through a virulence complex on the cell surface. This process, termed
cytoadherence, requires P. falciparum
to produce and export a range of proteins to the surface of the host
erythrocyte which possesses no endogenous protein trafficking apparatus. Membranous
parasite-derived structures called Maurer’s clefts that exist in the
erythrocyte cytoplasm play a key role in the sorting of proteins involved in
cytoadherence. Ring exported protein 1 (REX1) is a Maurer’s cleft protein
required for expression of the major virulence protein on the red blood cell
surface. The C terminal of REX1 contains a repeat region which varies between
parasite strains and diversity of these repeats is thought to be linked to parasite
virulence. In order to investigate the role of the C terminal repeat region of
REX1 in virulence protein trafficking, we have performed binding assays to
characterise the cytoadherence phenotype of several REX1 truncation,
replacement and wild type parasites. We have observed altered Maurer’s cleft structure
in parasites with deletion of the C terminal repeat region. Trypsin cleavage
assays, where the protease trypsin is used to cleave the extracellular portion
of the major virulence protein, have been performed to assess differences in
virulence protein surface expression.