Sexual stage-specific expression of a third calcium-dependent protein kinase from Plasmodium falciparum

A third calcium-dependent protein kinase (CDPK) gene has been isolated from the human malaria parasite Plasmodium falciparum by vectorette technology. The gene consists of five exons and four introns. The open reading frame r esulting from removal of the four introns encodes a protein of 562 amino ac id residues with a predicted molecular mass of 65.3 kDa. The encoded protei n, termed PfCDPK3, consists of four distinct domains characteristic of a me mber of the CDPK family and displays the highest homology (46% identity and 69% similarity) to PfCDPK2, the second CDPK of P. falciparum. The N-termin al variable domain is rich in serine/threonine and lysine and contains mult iple consensus phosphorylation sites for a range of protein kinases. The ca talytic domain possesses all conserved motifs of the protein kinase family except for the highly conserved glutamic acid residue in subdomain VIII, wh ich is replaced by a glutamine residue. The sequence of the junction domain comprising 31 amino acid residues is less conserved. The calmodulin-like r egulatory domain contains four EF-hand calcium-binding motifs, each consist ing of a loop of 12 amino acid residues which is flanked by two alpha-helic es. Southern blotting of genomic DNA digests showed that the Pfcdpk3 gene i s present as a single copy per haploid genome. A 2900 nucleotide transcript of this gene is expressed specifically in the sexual erythrocytic stage, i ndicating that PfCDPK3 is involved in sexual stage-specific events. It is p roposed that PfCDPK3 may serve as a link between calcium and gametogenesis of P. falciparum. (C) 2000 Elsevier Science B.V. All rights reserved.