Molecular and Biochemical Parasitology 107 (2000) 143 – 154 Characterization of domains of the phosphoriboprotein P0 of Plasmodium falciparum Sanchita Chatterjee a,1 , Subhash Singh 1a , Rashmi Sohoni a , Vidya Kattige a , Charusheela Deshpande a , Shubhada Chiplunkar b , Nirbhay Kumar c , Shobhona Sharma a, * a Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India b Cellular Immunology Unit, Cancer Research Institute, Parel, Mumbai 400 012, India c Department of Microbiology and Immunology, Johns Hopkins Uniersity, Baltimore, MD, USA Received 8 September 1999; received in revised form 25 November 1999; accepted 25 November 1999 Abstract Antibodies against the amino-terminal domain of the Plasmodium falciparum P0 phosphoriboprotein were detected extensively in immune people living in malaria endemic areas of India. It has been shown earlier that specific antibodies raised against the PfP0N domain (17 – 61 amino acid) of the PfP0 protein inhibit P. falciparum growth in vitro. To study the properties of the rest of the protein, the remaining 61–316 amino acids on the carboxy-side of the PfP0 protein were expressed as a glutathione-S-transferase fusion protein (PfP0C). Antibodies raised against PfP0C identified the 38 kDa P0 protein on a parasite Western blot analysis. An ELISA assay using both the PfP0N and PfP0C fusion proteins showed no reactivity with malaria patient sera samples, but showed extensive reactions with the immune sera. Antibodies against both the PfP0C and PfP0N domains were raised in rabbits and different inbred strains of mice. T-cells from immunized mice showed lymphoproliferation when presented with PfP0 protein domains. IgG from both anti-PfP0N and anti-PfP0C sera inhibited the growth of P. falciparum in vitro in a concentration dependent manner. The IgG did not show any significant effect on the growth of intraerythrocytic stages, but specifically inhibited re-invasion of red cells. Merozoites and sexual stages showed surface reactivity to both anti-PfP0N and anti-PfP0C antibodies in immunofluorescence assays. These properties strongly indicate PfP0 as a possible target for invasion-blocking antibodies. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Plasmodium falciparum; Ribosomal phosphoprotein P0; Malaria immunity; Immunogenicity; Surface localization www.elsevier.com/locate/parasitology Abbreiations: GST, glutathione-S-transferase; IPTG, Isopropyl -D-thiogalacto-pyranoside; PfP0, Plasmodium falciparum phos- phoriboprotein P0; PfP0C, carboxy-terminal domain of PfP0; PfP0N, amino-terminal domain of PfP0. * Corresponding author. Tel.: +91-22-2152971/2979, ext. 2570; fax: +91-22-2152110/2181. E-mail address: sharma@tifr.res.in (S. Sharma) 1 These two Authors contributed equally to this work. 0166-6851/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0166-6851(99)00226-1