Von Willebrand Factor A Domain-related Protein, a novel microneme protein of the malaria ookinete highly conserved throughout Plasmodium parasites

The mosquito-invasive form of the malarial parasite, the ookinete, develops numerous secretory organelles, called micronemes, in the apical cytoplasm. Micronemal proteins are thought to be secreted during midgut invasion and to play a crucial role in attachment and motility of the ookinete. We found a novel ookinete micronemal protein of rodent malarial parasite Plasmodium berghei, named P. berghei von Willebrand factor A domain-related protein ( PbWARP), and report it here as a putative soluble adhesive protein of the o okinete. The PbWARP gene contained a single open reading frame encoding a p utative secretory protein of 303 amino acids, with a von Willebrand factor type A module-like domain as a main component. Western blot analysis demons trated that PbWARP was firstly produced 12 h after fertilization by maturin g ookinetes as SDS-resistant complexes. Recombinant PbWARP produced with a baculovirus system also formed SDS-resistant high-order oligomers. Immuno-e lectron microscopic studies showed that PbWARP was randomly distributed in the micronemes. PbWARP homologues also exist in human malarial parasites, P lasmodium falciparum and Plasmodium vivax. Highly conserved primary structu res of PbWARP homologues among these phylogenetically distant Plasmodium sp ecies suggest their functional significance and the presence of a common in vasion mechanism widely utilized throughout Plasmodium parasites. (C) 2001 Elsevier Science B.V. All rights reserved.