Plant-like phosphofructokinase from Plasmodium falciparum belongs to a novel class of ATP-dependent enzymes

Abstract

Malaria parasite-infected erythrocytes exhibit enhanced glucose utilisation and 6-phospho-1-fructokinase (PFK) is a key enzyme in glycolysis. Here we present the characterisation of PFK from the human malaria parasite Plasmodium falciparum. Of the two putative PFK genes on chromosome 9 (PfPFK9) and 11 (PfPFK11), only the PfPFK9 gene appeared to possess all the catalytic features appropriate for PFK activity. The deduced PfPFK proteins contain domains homologous to the plant-like pyrophosphate (PPi)-dependent PFK β and α subunits, which are quite different from the human erythrocyte PFK protein. The PfPFK9 gene β and α regions were cloned and expressed as His₆- and GST-tagged proteins in Escherichia coli. Complementation of PFK-deficient E. coli and activity analysis of purified recombinant proteins confirmed that PfPFK9β possessed catalytic activity. Monoclonal antibodies against the recombinant β protein confirmed that the PfPFK9 protein has β and α domains fused into a 200 kDa protein, as opposed to the independent subunits found in plants. Despite an overall structural similarity to plant PPi-PFKs, the recombinant protein and the parasite extract exhibited only ATP-dependent enzyme activity, and none with PPi. Unlike host PFK, the Plasmodium PFK was insensitive to fructose-2,6-bisphosphate (F-2,6-bP), phosphoenolpyruvate (PEP) and citrate. A comparison of the deduced PFK proteins from several protozoan PFK genome databases implicates a unique class of ATP-dependent PFK present amongst the apicomplexan protozoans.