A unique phosphatidylinositol 4-phosphate 5-kinase is activated by ADP-ribosylation factor in Plasmodium falciparum.
In eukaryotes, calcium signalling has been linked to hydrolysis of the phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)). The final enzyme in the synthesis of this phosphoinositide, a Type I phosphatidylinositol 4-phosphate 5-kinase (PIP5K), is activated by the small G protein ADP-ribosylation factor 1 (ARF1). In mammals, the ARF-PIP5K pathway is a key regulator of cell motility, secretion and cell signalling. We report the characterisation of a unique, putative bifunctional PIP5K in the human malaria parasite Plasmodium falciparum. The protein comprises a C-terminal, functional PIP5K domain with catalytic specificity for phosphatidylinositol 4-phosphate. The recombinant enzyme is activated by ARF1 but not phosphatidic acid. The protein also incorporates an unusual N-terminal domain with potential helix-loop-helix EF-hand-like motifs that is a member of the neuronal calcium sensor family (NCS). Intriguingly, NCS-1 has been shown to stimulate phosphatidylinositol 4-phosphate synthesis by activating mammalian and yeast phosphatidylinositol 4-kinase beta in vitro in a calcium-dependent manner. The unexpected physical attachment of an NCS-like domain to the plasmodial PIP5K might reflect a unique functional link between the calcium and PtdIns(4,5)P(2) pathways allowing modulation of PtdIns(4,5)P(2) production in response to changes in intracellular calcium concentrations within the parasite.
Leber
Werner
W
Department of Infectious and Tropical Diseases, London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom. werner.leber@doctors.net.uk
Skippen
Alison
A
Fivelman
Quinton L
QL
Bowyer
Paul W
PW
Cockcroft
Shamshad
S
Baker
David A
DA
D020727:ADP-Ribosylation Factors / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D018257:Helix-Loop-Helix Motifs; D008969:Molecular Sequence Data; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D010963:Plasmodium falciparum / Q000201:enzymology*; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000378:metabolism*; D016415:Sequence Alignment; D013379:Substrate Specificity
D018129:Phosphatidylinositol Phosphates; D015800:Protozoan Proteins; C037178:phosphatidylinositol 4-phosphate; D017853:Phosphotransferases (Alcohol Group Acceptor); C020077:1-phosphatidylinositol-4-phosphate 5-kinase; D020727:ADP-Ribosylation Factors