Identification, Cloning, Expression, and Characterization of the Gene for Plasmodium knowlesi Surface Protein Containing an Altered Thrombospondin Repeat Domain

Division of Emerging and Transfusion Transmitted Diseases, Center for Biologics Evaluation and Research, Food and Drug Administration, 1401 Rockville Pike, Rockville, MD 20852, USA.
Infection and Immunity (Impact Factor: 3.73). 10/2005; 73(9):5402-9. DOI: 10.1128/IAI.73.9.5402-5409.2005
Source: PubMed


Proteins present on the surface of malaria parasites that participate in the process of invasion and adhesion to host cells are considered attractive vaccine targets. Aided by the availability of the partially completed genome sequence of the simian malaria parasite Plasmodium knowlesi, we have identified a 786-bp DNA sequence that encodes a 262-amino-acid-long protein, containing an altered version of the thrombospondin type I repeat domain (SPATR). Thrombospondin type 1 repeat domains participate in biologically diverse functions, such as cell attachment, mobility, proliferation, and extracellular protease activities. The SPATR from P. knowlesi (PkSPATR) shares 61% and 58% sequence identity with its Plasmodium falciparum and Plasmodium yoelii orthologs, respectively. By immunofluorescence analysis, we determined that PkSPATR is a multistage antigen that is expressed on the surface of P. knowlesi sporozoite and erythrocytic stage parasites. Recombinant PkSPATR produced in Escherichia coli binds to a human hepatoma cell line, HepG2, suggesting that PkSPATR is a parasite ligand that could be involved in sporozoite invasion of liver cells. Furthermore, recombinant PkSPATR reacted with pooled sera from P. knowlesi-infected rhesus monkeys, indicating that native PkSPATR is immunogenic during infection. Further efficacy evaluation studies in the P. knowlesi-rhesus monkey sporozoite challenge model will help to decide whether the SPATR molecule should be developed as a vaccine against human malarias.

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    • "In fact, it was previously demonstrated that recombinant SPATR from Plasmodium falciparum and its orthologue in P. knowlesi were able to bind to HepG2 cells with high specificity, and antibodies generated against SPATR could inhibit P. falciparum sporozoite invasion into liver cells [6,7]. The P. falciparum SPATR protein was recognized by sera from naturally infected Africans but not control sera from two non-immune donors, indicating that this protein was recognized by the host immune system [6]. "
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