Exploring inhibition of Pdx1, a component of the PLP synthase complex of the human malaria parasite Plasmodium falciparum

Abstract

Malaria tropica is a devastating infectious disease caused by Plasmodium falciparum. This parasite synthesizes vitamin B6 de novo via the pyridoxal 5-phosphate (PLP) synthase enzymatic complex consisting of PfPdx1 and PfPdx2 proteins. Biosynthesis of PLP is largely performed by PfPdx1, ammonia provided by PfPdx2 subunits, is condensed together with Dribose 5-phosphate (R5P) and DL-glyceraldehyde 3-phosphate (G3P). PfPdx1 accommodates both the R5P and G3P substrates and intricately coordinates the reaction mechanism, which is composed of a series of imine bond formations, leading to the production of PLP. We demonstrate that D-erythrose 4-phosphate (E4P) inhibits PfPdx1 in a dose dependent manner. We propose that the acyclic phospho-sugar E4P, with a C1 aldehyde group similar to acyclic R5P, could interfere with R5P imine bond formations in the PfPdx1 reaction mechanism. Molecular docking and subsequent screening identified the E4P hydrazide analogue, 4- phospho-D-erythronhydrazide (4PEHz), which selectively inhibited PfPdx1 with an IC50 of 43 μM. PfPdx1 contained in the heteromeric PLP synthase complex was shown to be more sensitive to 4PEHz and was inhibited with an IC50 of 16 μM. Moreover, the compound had an IC50 value of 10 μM against cultured P. falciparum intraerythrocytic parasites. To further analyse the selectivity of 4PEHz, transgenic cell lines over-expressing PfPdx1 and PfPdx2 showed that additional copies of the protein complex conferred protection against 4PEHz, implicating that the PLP synthase is directly affected by 4EPHz in vivo. These PfPdx1 inhibitors represent novel lead scaffolds which are capable of targeting PLP biosynthesis, and we propose this as a viable strategy for the development of newer therapeutics against malaria.