title: Plasmodium falciparum pyruvate kinase as a novel target for antimalarial drug-screening.
abstract: BACKGROUND
  Global travellers are increasingly at risk of contracting malaria. The increasing occurrence of drug-resistance in many endemic areas emphasizes the need for novel drug targets for antimalarial-screening. In this study, the use of pyruvate kinase as a drug-target is evaluated. The functional validation of a gene encoding pyruvate kinase (designated PK1) has previously been reported. However, alternative copies of this enzyme encoded by Plasmodium falciparum could also circumvent the role of PK1. A survey of genome data revealed a putative ORF seemingly coding for another pyruvate kinase (designated PK2).
  
  
  METHODS
  The expression of PK1 and PK2 in in vitro cultures were investigated by RT-PCR. Biocomputational analysis was carried out to identify structural differences between the P. falciparum pyruvate kinases and the corresponding enzymes from its human host.
  
  
  RESULTS
  Both PK1 and PK2 were indeed actively transcribed during the intraerythrocytic stages, suggesting the involvement of both enzymes during infection. A comparison of amino acid residues at the effector binding sites of PK1 and PK2, to those of the human pyruvate kinases revealed some significant differences that could serve as targets for selective inhibitors to be designed against parasitic pyruvate kinases.
  
  
  CONCLUSIONS
  Experimental evidence for the expression of both PK1 and PK2 during the blood stages of malaria infection was provided. Interestingly, phylogenetic analysis revealed that the "PK2" type of enzyme appears to be confined to Apicomplexans, an important observation with respect to the assessment of PK2 as a drug-target.
authors.affiliation: Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, Block MD4, 5 Science Drive 2, Singapore 117597, Singapore.
authors.forename: Maurice
authors.initials: M
authors.lastname: Chan
authors.forename: Doreen S H
authors.initials: DS
authors.lastname: Tan
authors.forename: T S
authors.initials: TS
authors.lastname: Sim
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000962:Antimalarials / Q000627:therapeutic use*; D004353:Drug Evaluation, Preclinical; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D006801:Humans; D016778:Malaria, Falciparum / Q000188:drug therapy* / Q000469:parasitology; D008969:Molecular Sequence Data; D010963:Plasmodium falciparum / Q000201:enzymology* / Q000235:genetics; D011770:Pyruvate Kinase / Q000032:analysis* / Q000235:genetics; D016415:Sequence Alignment
chemical_list: D000962:Antimalarials; D011770:Pyruvate Kinase