title: Cloning, expression, and immunocharacterization of surface protein containing an altered thrombospondin repeat domain (SPATR) from Plasmodium knowlesi.
abstract: BACKGROUND
  Plasmodium knowlesi is the fifth species identified to cause malaria in humans and is often misdiagnosed as Plasmodium malariae due to morphological similarities. The development of an inexpensive, serological detection method utilizing antibodies specific to P. knowlesi would be a valuable tool for diagnosis. However, the identification of specific antigens for these parasites remains a major challenge for generating such assays. In this study, surface protein containing an altered thrombospondin repeat domain (SPATR) was selected as a potentially specific antigen from P. knowlesi. Its multistage expression by sporozoites, asexual erythrocytic forms and gametocytes, along with its possible role in liver cell invasion, suggests that SPATR could be used as a biomarker for diagnosis of P. knowlesi.
  
  
  METHODS
  The spatr gene from P. knowlesi was codon optimized and cloned (pkhspatr). Recombinant pkHSPATR protein was expressed, purified, and evaluated for its sensitivity and specificity in immunoblot and ELISA-based assays for detecting P. knowlesi infection.
  
  
  RESULTS
  The recombinant pkHSPATR protein allows sensitive detection of human P. knowlesi infection in serum samples by immunoblot and ELISA.
  
  
  CONCLUSIONS
  With further research, recombinant pkHSPATR protein could be exploited as a marker for detection of P. knowlesi infection in humans. Therefore, this finding should contribute to the development of immunodiagnostic assays for the species-specific detection of malaria.
authors.affiliation: Department of Parasitology, TIDREC, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia.
authors.forename: Vanitha
authors.initials: V
authors.lastname: Palaeya
authors.forename: Yee Ling
authors.initials: YL
authors.lastname: Lau
authors.forename: Rohela
authors.initials: R
authors.lastname: Mahmud
authors.forename: Yeng
authors.initials: Y
authors.lastname: Chen
authors.forename: Mun Yik
authors.initials: MY
authors.lastname: Fong
mesh_terms: D000913:Antibodies, Protozoan / Q000097:blood*; D000953:Antigens, Protozoan / Q000235:genetics / Q000276:immunology; D019411:Clinical Laboratory Techniques / Q000379:methods*; D003001:Cloning, Molecular; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D015870:Gene Expression; D006801:Humans; D015151:Immunoblotting / Q000379:methods; D008288:Malaria / Q000175:diagnosis* / Q000469:parasitology; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology; D010274:Parasitology / Q000379:methods*; D016790:Plasmodium knowlesi / Q000235:genetics / Q000276:immunology*; D011994:Recombinant Proteins / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification; D012680:Sensitivity and Specificity
chemical_list: D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D008565:Membrane Proteins; D011994:Recombinant Proteins; C504428:SPATR protein, Plasmodium knowlesi