Summary:
Plasmodium falciparum causes severe malaria and about 2 million human deaths
annually. The main obstacle to combat the disease is increasing resistance of
the parasites to existing drugs and the lack of a protective vaccine. Therefore,
it is imperative that new suitable drug targets in the parasite`s metabolism are
identified, assessed and validated. The availability of the parasite`s genome
sequence offers an excellent tool to identify metabolic pathways potentially
essential for parasite survival. Scrutinising the Plasmodium genomes revealed
that they possess biosynthetic pathways for vitamins. Vitamins are organic
compounds required in small amounts to ensure normal metabolic functions. Since
they are not synthesised by humans, they need to be supplied via nutrients in
trace amounts. The absence of vitamin biosynthesis in humans suggests that
specific targeting of these parasite pathways with inhibitors is feasible. Thus,
vitamin biosynthesis of Plasmodium might offer excellent potential for the
development of novel chemotherapeutics against malaria with specific toxicity
towards the parasites without affecting the host’s metabolism. In the first
instance, we will focus on vitamin B6 biosynthesis, as this important nutrient
is required as a co-factor for a wide variety of essential metabolic functions
in protein and amino acid metabolism, and has also has been implicated in the
defence against oxidative stress in other eukaryotes. Using reverse genetic
approaches, we will validate the suitability of two of the vitamin B6
synthesising enzymes Pdx1 and Pdx2 respectively as drug targets. In addition,
their precise biological functions and potential interactions with other
cellular components will be analysed. Further, the biochemical, biophysical and
structural features of both enzymes will be assessed in order to be able to
rationally design specific inhibitors that interfere with the parasite’s
proteins activities and functions.
Background:
As P. falciparum, the most dangerous human malaria parasite, is
rapidly developing resistances against most of the currently available drugs,
there is an urgent need to identify new targets in Plasmodium metabolism
that can be specifically inhibited without affecting the human host. One of
these might be vitamin biosynthesis. Vitamins belonging to the vitamin B complex
such as thiamine (B1), riboflavin (B2), pyridoxine (B6) and cobalamin (B12)
cannot be synthesised by mammals and have to be taken up in their diet. In
contrast, micro-organisms, including the malarial parasites, fungi and plants,
possess de novo biosynthetic pathways that provide these organisms with
an intrinsic source of these essential compounds. Of all the water-soluble
vitamins that are present in blood plasma, the only one for which the
intracellular parasite apparently has an absolute requirement and for which the
parasitised cell must consequently have the appropriate uptake system, is B5,
the precursor of coenzyme A. Therefore, there is a hypothesis that the parasites
most likely possess biosynthetic pathways for the other water-soluble vitamins.
This hypothesis is supported by the presence of genes in the parasite genome
that encode proteins and enzymes necessary for the biosynthesis of a number of
vitamins, including those for lipoic acid synthesis, the vitamin and coenzyme
precursor chorismate and vitamin B6 biosynthesis.
Aim:
Validation of vitamin B 6 biosynthesis as the novel target for antimalarial
drug development.
Expected results:
- Assessment of the biological and physiological function of vitamin B6 in
P. falciparum
- Biochemical and biophysical characterisation of enzymes involved in vitamin
B6 biosynthesis in P. falciparum
- Identification and characterisation of protein-protein interactions between
vitamin B6 biosynthetic enzymes and other cellular components
- Structural characterisation of the enzymes of P. falciparum vitamin
B6 biosynthesis in order to obtain thorough insight into the mechanisms of
action of the proteins.
Potential applications:
Antimalarial and possibly anti-apicomplexan drug development.
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