TgGloL is an atypical glyoxalase domain-containing apicoplast protein that is important for the growth of Toxoplasma

Glycolysis is a conserved metabolic pathway that typically converts glucose into pyruvate in the cytosol, generating ATP and the reducing agent NADH. Like in plants, in Toxoplasma gondii and several other apicomplexan parasites some cytosolic glycolytic enzymes also have isoforms which are located in their plastid (called the apicoplast in apicomplexans). Noticeably, the glycolytic intermediates glyceraldehyde 3-phosphate (GA3P) and dihydroxy acetone phosphate (DHAP) are imported from the cytosol and metabolized further by these glycolytic enzymes in the apicoplast, presumably to provide ATP and reducing power, but also to generate precursors for anabolic pathways like isoprenoid synthesis. However, GA3P and DHAP can spontaneously convert into methylglyoxal, a highly reactive and very cytotoxic by-product. Methylglyoxal is detoxified principally via the glyoxalase system which consists of the enzymes Glyoxalase-1 (Glo-1) and Glyoxalase-2 (Glo-2).

In addition to the canonical Glo-1 and Glo-2 present in the cytosol of T. gondii, we have identified an atypical protein that contains a Glo-1-like motif but has a very limited overall homology with typical Glo enzymes. We have shown that this protein localizes to the apicoplast and by generating a conditional knock-down cell line, we have demonstrated that it is important for optimal parasite growth. These results suggest that there might be a specific system for detoxifying derivatives of glycolytic intermediates in the apicoplast, and that this system is important for maintaining parasite fitness.