J Biol Chem. 2007 Aug 27; [Epub ahead of print]
The farnesyl diphosphate/geranylgeranyl diphosphate synthase of toxoplasma gondii is a bifunctional enzyme and a molecular target of bisphosphonates
Ling Y, Li ZH, Miranda K, Oldfield E, Moreno SN
Cellular Biology, University of Georgia, Athens, GA 30606.
Farnesyl diphosphate synthase (FPPSs) catalyzes the synthesis of farnesyl diphosphate (FPP), an important precursor of sterols, dolichols, ubiquinones and prenylated proteins. We report the cloning and characterization of two Toxoplasma gondii farnesyl diphosphate synthase (TgFPPS) homologs. A single genetic locus produces two transcripts, TgFPPS and TgFPPSi, by alternative splicing. Both isoforms were heterologously expressed in Escherichia coli, but only TgFPPS was active. The protein products predicted from the nucleotide sequences have 646 and 605 amino acids and apparent molecular masses of 69.5 and 64.5 kDa, respectively. Several conserved sequence motifs found in other prenyl diphosphate synthases are present in both TgFPPSs. TgFPPS was also expressed in the baculovirus system and was biochemically characterized. In contrast to the FPPSs of other eukaryotic organisms, TgFPPS is bifunctional, catalyzing the formation of both farnesyl diphosphate (FPP) and geranylgeranyl diphosphate (GGPP). TgFPPS localizes to the mitochondria, as determined by the co-localization of the reaction of affinity-purified antibodies against the protein with MitoTracker, and in accord with the presence of an N-terminal mitochondrial-targeting signal in the protein. This enzyme is an attractive target for drug development, since the order of inhibition of the enzyme by a number of bisphosphonates is the same to that for inhibition of parasite growth. In summary, we report the first bifunctional farnesyl diphosphate/geranylgeranyl diphosphate synthase identified in eukaryotes, which, together with previous results, establishes this enzyme as a valid target for the chemotherapy of toxoplasmosis.
PMID: 17724033 [PubMed - as supplied by publisher]