Carotenoid Biosynthesis in Intraerythrocytic Stages of Plasmodium falciparum

Abstract

Carotenoids are widespread lipophilic pigments synthesized by all photosynthetic organisms and some nonphotosynthetic fungi and bacteria. All carotenoids are derived from the C40 isoprenoid precursor geranylgeranyl pyrophosphate, and their chemical and physical properties are associated with light absorption, free radical scavenging, and antioxidant activity. Carotenoids are generally synthesized in well defined subcellular organelles, the plastids, which are also present in the phylum Apicomplexa, which comprises a number of important human parasites, such as Plasmodium and Toxoplasma. Recently, it was demonstrated that Toxoplasma gondii synthesizes abscisic acid. We therefore asked if Plasmodium falciparum is also capable of synthesizing carotenoids. Herein, biochemical findings demonstrated the presence of carotenoid biosynthesis in the intraerythrocytic stages of the apicomplexan parasite P. falciparum. Using metabolic labeling with radioisotopes, in vitro inhibition tests with norflurazon, a specific inhibitor of plant carotenoid biosynthesis, the results showed that intraerythrocytic stages of P. falciparum synthesize carotenoid compounds. A plasmodial enzyme that presented phytoene synthase activity was also identified and characterized. These findings not only contribute to the current understanding of P. falciparum evolution but shed light on a pathway that could serve as a chemotherapeutic target.

Lipophilic analogs of zoledronate and risedronate inhibit Plasmodium geranylgeranyl diphosphate synthase (GGPPS) and exhibit potent antimalarial activity

“…DMAPP then condenses sequentially with three molecules of IPP to form geranyl diphosphate (GPP), farnesyl diphosphate (FPP), and geranylgeranyl diphosphate (GGPP), which is then used to prenylate proteins (26). In addition, in P. falciparum, GGPP is converted via prephytoene diphosphate to phytoene and then to carotenoids (27); plus, the longer-chain diphosphates are converted to quinones such as Men-4 (28) as well as dolichols (29). In Plasmodium spp., GGPPS appears to be bifunctional, making both FPP as well as GGPP; but based on its sequence and X-ray crystallographic structure with bound inhibitors (16), the enzyme is clearly more similar to other farnesyl diphosphate synthase (FPPS) than GGPPS enzymes-as evidenced, for example, by the presence of a third Asp in the second conserved DDXXD-domain (16), inhibition by zoledronate and risedronate (unlike human and Saccharomyces cerevisae GGPPS), and the presence of the 3Mg 2þ seen in these structures, compared to the 2Mg 2þ typically found in S. cerevisae GGPPS (30).…”

Isoprenoid Biosynthesis in Plasmodium falciparum

“…Norflurazon treatment causes an accumulation of phytoene and a decrease in carotenoid content. Inhibition by norflurazon can be partially rescued with lycopene (104). While carotenoids serve important functions in plants, algae, bacteria, and fungi, it is not yet known what physiological role they play in Plasmodium.…”

“…Carotenoids have recently been detected in the intraerythrocytic stages of P. falciparum; schizonts contain the highest concentrations, indicating that carotenoid synthesis begins in the ring stage and builds during the schizont stage (104). Geranyl pyrophosphate serves as a substrate for carotenoid synthesis by phytoene synthase (EC 2.5.1.32, PlasmoDB ID PF3D7_0202700).…”

“…The parasite possesses an octaprenyl pyrophosphate synthase (EC 2.5.1.90, PlasmoDB ID PF3D7_0202700) that is capable of synthesizing these side chains. This multifunctional enzyme produces 40-carbon, 45-carbon, and 55-carbon isoprenoid products and has been shown to also have phytoene synthase activity (104,117). The addition of these isoprenoids to 4-hydroxybenzoate is performed by 4-hydroxybenzoate octaprenyltransferase (EC 2.5.1.39, PlasmoDB ID PF3D7_0607500) (118,119).…”

Use of Radioactive Precursors for Biochemical Characterization the Biosynthesis of Isoprenoids in Intraerythrocytic Stages of Plasmodium falciparum

“…HPLC analysis from extracts of intraerythrocytic stages of P. falciparum labeled with [1-(n)-3 H]GGPP, revealed several compounds in all intraerythrocytic stages, with retention times coincident with lutein, phytoene, phytofluene, all-trans--carotene, neurosporene and 6-all-trans-lycopene. Some of these compounds were structurally characterized by electrospray mass spectrometric analysis (Tonhosolo et al, 2009). Considering that carotenoid biosynthesis is absent in humans, and also that possibly other uncharacterized carotenoid synthesizing enzymes are present, in Plasmodium, it possible to speculate that this pathway could be exploited for the design of new antimalarial drugs.…”