Malaria is responsible for the death of more than 600,000 people annually, mostly in the age group 0 - 5 years. Current antimalarial drug classes are compromised by emerging resistance. I will present recent findings from our lab underpinning efforts to develop a new antimalarial strategy. I will also present new finding on the cell biology of the transmissible stage of Plasmodium falciparum.
In an effort to overcome the increasing levels of resistance to artemisinins and partner drugs, we screened a series of nucleoside sulfamates from the Takeda Pharmaceuticals library and identified compounds that exhibit high potency against P. falciparum blood stage cultures, high selectivity against mammalian cell lines and long half-lives in blood. An exemplar compound demonstrates multi-stage activity and single dose efficacy in the P. falciparum SCID mouse model. Using in vitro evolution of resistance, we have identified the target as P. falciparum tyrosyl-tRNA synthetase (PfTyr-RS). PfTyr-RS catalyses the formation of a highly stable inhibitory sulfamate conjugate, via a mechanism we call reaction-hijacking. Enzyme kinetics and X-ray crystallographic studies of plasmodium and human Tyr-RS reveal that differential flexibility of a loop over the catalytic site determines differential susceptibility to inhibition by nucleoside sulfamates. The work points to the potential for the design of bespoke nucleoside sulfamates, with tuneable specificity for applications in a broad range of infectious diseases.

The sexual stage gametocytes of the malaria parasite, Plasmodium falciparum, adopt an falciform (crescent) shape driven by the assembly of a network of microtubules anchored onto a cisternal structure termed the inner membrane complex (IMC). Using optical and electron microscopy, we show that a non-mitotic microtubule organizing center (MTOC) that is embedded in the parasite’s nuclear membrane orients the endoplasmic reticulum and the nascent IMC and seeds cytoplasmic microtubules early in gametocyte development. A dense bundle of microtubules extends into the nuclear lumen, elongating and distorting the nuclear envelope and capturing and organizing the chromatin. Classical components of the mitotic machinery, including the centriolar plaque proteins Pfcentrin-1 and -4, the microtubule-associated protein, End Binding protein-1, the kinetochore protein, PfNDC80, and the centromere-associated protein, PfCENH3, are involved in the assembly/disassembly process. Depolymerisation of the microtubules using trifluralin prevents elongation and disrupts the chromatin, centromere and kinetochore organisation, suggesting that this unusual non-mitotic hemispindle plays a central role in chromatin organization, IMC positioning and subpellicular microtubule formation in gametocytes.