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.
