Structural analyses of <i>Trichomonas vaginalis</i> pyrophosphate-dependent phosphofructokinase ( <i>Tv</i> PPi-PFK)

Abstract Trichomonas vaginalis causes trichomoniasis, the most common non-viral sexually transmitted disease in humans. T. vaginalis pyrophosphate-dependent phosphofructokinase ( Tv PPi-PFK) is a putative target for rational, structure-based drug discovery, given its absence in mammals and its importance for parasite survival. Tv PPi-PFK is a cytosolic enzyme that catalyzes the phosphorylation of fructose-6-phosphate using pyrophosphate (PPi) as the phosphoryl donor. This reversible reaction, catalyzed by Tv PPi-PFK, is the first committed step in glycolysis. Its reverse reaction is vital for gluconeogenesis in T. vaginalis . The purification, crystallization, structure determination, and preliminary structure-functional analyses of three crystal structures of Tv PPi-PFK are presented. All three structures organize as tetramers with the conserved motifs essential for pyrophosphate binding and PPi-PFK catalytic activity. Comparative analysis with structural neighbors from other organisms demonstrated that despite sharing &lt;29% sequence identity, Tv PPi-PFK’s protomer shares overall topology with both PPi- and ATP-dependent PFKs. Mass photometry confirmed that Tv PPi-PFK formed tetramers under near-physiological conditions. Unexpectedly, Tv PPi-PFK crystals dephosphorylate ATP to AMP during soaking. In all three structures, either ATP or AMP is bound at the enzyme’s dimer interface, typical of ATP-PFKs, but a novel finding for PPi-PFKs. Furthermore, a sugar phosphate binding site was observed in proximity to the ATP-binding site. Thus, the three reported Tv PPi-PFK structures validate its established PPi-dependent activity while revealing previously unreported ATP and sugar phosphate binding. This study also lays a foundation for future research into putative ATP-dependent activity of Tv PPi-PFK and for evaluating known phosphofructokinase inhibitors as potential therapeutics for trichomoniasis. These findings expand our understanding of PFK superfamily diversity and support the continued exploration of Tv PPi-PFK as a drug target for trichomoniasis. Synopsis The production, crystallization, and three crystal structures of a pyrophosphate-dependent phosphofructokinase from Trichomonas vaginalis ( Tv PPi-PFK) reveal ATP binding and structural similarity to both ATP-dependent and pyrophosphate-dependent phosphofructokinases. Tv PPi-PFK dephosphorylates ATP and has a novel ATP-PFK-like ATP-binding cavity.