Characterization of the Plasmodium falciparum replication licensing factor,

Fredrick Lunyagi Eyase


Malaria remains a big challenge the world-over especially in Sub-sahara Africa. Since
there is no malaria vaccine currently, chemotherapy is the only curative intervention
option available. At present, there are few known drug targets in the parasite. Worse
still, most of these targets have mutated leading to widespread resistance to current
drugs. There is therefore an urgent need for discovery and development of new
antimalarial chemotherapeutic interventions and targets. An “Achilles' heel” in the
parasite biology that could be exploited for chemotherapeutic intervention is the
parasite cell cycle mechanisms. Thus, recent malaria drug discovery efforts have
focused on targeting parasite-derived cyclin-dependent kinase proteins as potential
new drug targets. The aim of this study was therefore to to establish the functional
relationships between two of these kinases, PfMRK and PfPK6, with a putative P.
falciparum replication licensing factor (PfRLF) with a view of establishing their
potential as drug targets.
A non-radiactive kinase assay was used to assess phosphorylation capacities of
PfMRK and PfPK6 on PfRLF. Bioinformatic tools were also used to characterize
PfRLF. Kinase inhibition assays using locally sourced natural products as inhibitors
to PfMRK and PfPK6 were carried out to unravel the drug target potential of these
kinanses. Bioinformatic analyses revealed that the putative PfRLF is actually the
P.falciparum Minichromosome Maintenance 6 (PfMCM6) protein involved in
replication. The kinase assays established that both PfPK6 and PfMRK phosphorylate
PfMCM6 in vitro and that PfMAT1 enhances PfMRK activity on PfMCM6.
Enhancement of PfMRK activity by PfMAT1 confirms previous observations that PfMRK is the plasmodial CDK7 equivalent. The Kinase inhibition assays showed that
the Abyssinone class of flavonoids actively inhibits the activity of PfMRK and PfPK6
on PfMCM6.
This study has confirmed the potential of PfMRK and PfPK6 as drug targets for
malaria treatment. Flavonoids, especially prenylated abyssinones are lead compounds
for antimalarials targeting these two kinases. Modification and further
characterization of these lead compounds may lead to therapeutic agents with higher
efficacy and specificity


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