Cobbold, S. | Search bioRxiv

bioRxiv2022

PTEX helps efficiently traffic haemoglobinases to the food vacuole in Plasmodium falciparum.

A key element of Plasmodium biology and pathogenesis is the trafficking of ~10% of the parasite proteome into the host red blood cell (RBC) it infects. To cross the parasite-encasing parasitophorous vacuole membrane, exported proteins utilise a channel-containing protein complex termed the Plasmodium translocon of exported proteins (PTEX). PTEX is obligatory for parasite survival, both in vitro and in vivo, suggesting that at least some exported proteins have essential metabolic functions. However, to date only one essential PTEX-dependent process, the new permeability pathway, has been described. To identify other essential PTEX-dependant proteins/processes, we conditionally knocked down the expression of one of its core components, PTEX150, and examined which metabolic pathways were affected. Surprisingly, the food vacuole mediated process of haemoglobin (Hb) digestion was substantially perturbed by PTEX150 knockdown. Using a range of transgenic parasite lines and approaches, we show that two major Hb proteases; falcipain 2a and plasmepsin II, interact with PTEX core components, implicating the translocons involvement in the trafficking of Hb proteases. We propose a model where these proteases are translocated into the PV via PTEX in order to reach the cytostome, located at the parasite periphery, prior to food vacuole entry. This work offers a another mechanistic explanation for why PTEX function is essential for growth of the parasite within its host RBC. Author summaryPlasmodium falciparum is the causative agent of the most severe form of malaria in humans, where the symptoms of the disease are derived from the continuous asexual replication of the parasite within the human red blood cells (RBCs) it infects. To survive within this niche, the parasite exports hundreds of parasite effector proteins across the vacuole it resides within and into the RBC. About a quarter of the exported proteins appear to be essential during the blood stage but the functions of these proteins largely remain uncharacterised. Protein export is facilitated by an essential protein complex termed the Plasmodium translocon of exported proteins (PTEX). Conditional depletion of PTEXs core components results in rapid parasite death presumably because essential proteins do not reach their functional destination in the RBC and their associated metabolic functions cannot be performed. To uncover what these essential metabolic functions are we knocked down PTEX150, a core component of PTEX. Metabolic analysis of the knockdown parasites indicated that haemoglobin (Hb) digestion was inhibited resulting in a reduction of Hb derived peptides, which serve as an amino acid source for the parasite. We determined that knocking down HSP101, another PTEX core component, also disrupted the Hb digestion pathway. Furthermore, we provide evidence that reduction of Hb digestion might be due to the failure to efficiently deliver early acting Hb digesting proteases to the cytostome, a specialised location where vesicles of Hb are taken into the parasite. PTEX may therefore play a role in delivering Hb proteases to the cytostome.

microbiology↗

bioRxiv2018

The metabolic repair enzyme phospho-glycolate phosphatase regulates central carbon metabolism and fosmidomycin sensitivity in Plasmodium falciparum

The asexual blood stages of the malaria parasite, Plasmodium falciparum are highly dependent on glycolysis for ATP synthesis, redox balance and provision of essential anabolic precursors. Recent studies have suggested that members of the haloacid dehalogenase (HAD) family of metabolite phosphatases may play an important role in regulating multiple pathways in P. falciparum central carbon metabolism. Here, we show that the P. falciparum HAD protein, phosphoglycolate phosphatase (PfPGP), which is homologous to yeast Pho13 and mammalian PGP, regulates glycolysis in asexual blood stages by controlling intracellular levels of several intermediates and novel end-products of this pathway. Deletion of the P. falciparum pgp gene significantly attenuated asexual parasite growth in red blood cells, while comprehensive metabolomic analysis revealed the accumulation of two previously uncharacterized metabolites, as well as changes in a number of intermediates in glycolysis and the pentose phosphate pathway. The two unknown metabolites were assigned as 2-phospho-lactate and 4-phosphoerythronate by comparison of their mass spectra with synthetic standards. 2-Phospho-lactate was significantly elevated in wildtype and {Delta}PfPGP parasites cultivated in the presence of methylglyoxal and D-lactate, but not L-lactate, indicating that it is a novel end-product of the methylglyoxal pathway. 4-Phosphoerythronate is a putative side product of the glycolytic enzyme, glyceraldehyde dehydrogenase and the accumulation of both 4-phosphoerythronate and 2-phospho-D-lactate were associated with changes in glycolytic and the pentose phosphate pathway fluxes as shown by 13C-glucose labelling studies and increased sensitivity of the {Delta}PfPGP parasites to the drug fosmidomycin. Our results suggest that PfPGP contributes to a novel futile metabolic cycle involving the phosphorylation/dephosphorylation of D-lactate as well as detoxification of metabolites, such as 4-phosphoerythronate, and both may have important roles in regulating P. falciparum central carbon metabolism.\n\nAuthor summaryThe major pathogenic stages of the malaria parasite, Plasmodium falciparum, develop in red blood cells where they have access to an abundant supply of glucose. Unsurprisingly these parasite stages are addicted to using glucose, which is catabolized in the glycolytic and the pentose phosphate pathways. While these pathways also exist in host cells, there is increasing evidence that P. falciparum has evolved novel ways for regulating glucose metabolism that could be targeted by next-generation of anti-malarial drugs. In this study, we show the red blood cell stages of P. falciparum express an enzyme that is specifically involved in regulating the intracellular levels of two metabolites that are novel end-products or side products of glycolysis. Parasite mutants lacking this enzyme are viable but exhibit diminished growth rates in red blood cells. These mutant lines accumulate the two metabolites, and exhibit global changes in central carbon metabolism. Our findings suggest that metabolic end/side products of glycolysis directly regulate the metabolism of these parasites, and that the intracellular levels of these are tightly controlled by previously uncharacterized metabolite phosphatases.

biochemistry↗