Abstract
Many biosynthetic pathways produce pyrophosphate (PPi) as a by-product, which is cytotoxic if accumulated at high levels. Pyrophosphatases play pivotal roles in PPi detoxification by converting PPi to inorganic phosphate. A number of apicomplexan parasites, including Toxoplasma gondii and Cryptosporidium parvum, express a PPi-dependent phosphofructokinase (PPi-PFK) that consumes PPi to power the phosphorylation of fructose-6-phosphate. However, the physiological roles of PPi-PFKs in these organisms are not known. Here, we report that Toxoplasma expresses both ATP- and PPi-dependent phosphofructokinases in the cytoplasm. Nonetheless, only PPi-PFK was indispensable for parasite growth, whereas the deletion of ATP-PFK did not affect parasite proliferation or virulence. The conditional depletion of PPi-PFK completely arrested parasite growth, but it did not affect the ATP level and only modestly reduced the flux of central carbon metabolism. However, PPi-PFK depletion caused a significant increase in cellular PPi and decreased the rates of nascent protein synthesis. The expression of a cytosolic pyrophosphatase in the PPi-PFK depletion mutant reduced its PPi level and increased the protein synthesis rate, therefore partially rescuing its growth. These results suggest that PPi-PFK has a major role in maintaining pyrophosphate homeostasis in T. gondii. This role may allow PPi-PFK to fine-tune the balance of catabolism and anabolism and maximize the utilization efficiency for carbon nutrients derived from host cells, increasing the success of parasitism. Moreover, PPi-PFK is essential for parasite propagation and virulence in vivo but it is not present in human hosts, making it a potential drug target to combat toxoplasmosis.
Highlights
Inorganic pyrophosphate (PPi) is a ubiquitous metabolite in cells [1,2]
Different from classic ATP-dependent phosphofructokinases, PPi-dependent phosphofructokinase (PPi-PFK) use pyrophosphate consumption to power the conversion of fructose-6-phosphate to fructose-1,6bisphosphate, the committed step of glycolysis
Using the Toxoplasma gondii parasite as a model, here we show that PPi-PFK has a coordinator function to assure matched activities of anabolism and catabolism
Summary
Inorganic pyrophosphate (PPi) is a ubiquitous metabolite in cells [1,2]. It can be generated by diverse biosynthetic reactions, including the synthesis of proteins, DNA, RNA, isoprenoids, polysaccharides, etc. The abnormal accumulation of PPi is toxic to cells, likely because high levels of PPi are unfavorable for the reactions that generate this compound [6]. One common mechanism for regulating PPi levels is through hydrolysis catalyzed by pyrophosphatases (PPases). In plants and some bacteria and protozoa, PPi hydrolysis can be catalyzed by pyrophosphate-dependent phosphofructokinases (PPiPFKs), which use PPi as the energy and phosphate donor to catalyze the conversion of fructose-6-phosphate (F6P) to fructose-1,6-bisphosphate (FBP) [10,11,12,13]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
