Cloning and characterization of a new asparagine-rich protein in Plasmodium falciparum

A cDNA clone that encodes a Plasmodium falciparum asparagine (N)-rich protein (PfARP) was isolated through immunoscreening of an expression library. A 9.4 kb PfARP transcript was identified by Northern blot hybridization and the gene was localized on chromosome 1. The complete coding sequence (6666 bp) revealed a protein that contains clustered as well as randomly distributed N residues (24.3%), seven copies of a repeat sequence [DNT(D/N)(K/N)(V/L/M)] and multiple copies of tripeptide repeats within a 101 amino acid region containing 89 D/E residues. The PfARP was immunogenic in inbred and outbred mice and endemic sera revealed the presence of low-titer antibodies against PfARP. Anti-PfARP sera showed cytoplasmic and surface localization of apparently cross-reactive malarial antigens in different life-cycle stages (ring, trophozoite, schizont, and gametocytes). Although the biological function(s) of PfARP are not known, the observation that it is present in multiple parasite stages and that it is a target of natural immune response warrants further study of PfARP as an immune target.