Discovery and validation of inhibitors targeting protein-protein interactions in the plasmodial glideosome
Boucher, Lauren Elizabeth
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Plasmodium falciparum is the parasite responsible for the most deadly cases of malaria in humans. Emerging resistance of P. falciparum to available treatments is of concern, and necessitates the development of novel compounds targeting the parasite. Traditional drug development has been geared towards developing inhibitors of enzymes essential to the parasite. Alternatively, we have chosen to target an essential protein-protein interaction (PPI). In developing novel inhibitory and probe compounds, we chose to target the invasion machinery, also known as the glideosome. P. falciparum uses an actomyosin motor, part of the glideosome complex, to invade multiple cell types. A key component of the machinery is a tetrameric complex of aldolase that binds the cytoplasmic, C-terminal tail of the transmembrane adhesive protein, TRAP (thrombospondin related anonymous protein). Different TRAPs are required for invasion of different host cells: TRAP (liver stage), MTRAP (blood stage) and CTRAP (mosquito stage). The dynamic aldolase-TRAP complex must dissociate periodically as invasion progresses. By targeting the aldolase-TRAP interaction with a small molecule drug that tightens this interaction, we can select for a compound that can inhibit invasion. To identify novel small molecules, we have developed a system to produce TRAP peptides and use surface plasmon resonance to screen the Medicines for Malaria Venture’s (MMV) Malaria Box compound library against the aldolase-TRAP interaction. We have validated compound hits targeting this interaction in sporozoite gliding assays, live imaging studies, and using liver invasion assays. One compound has been found to reduce levels of sporozoite invasion of HepG2 cells and reduce levels and speed of gliding. Attempts have been made to co-crystallize the compound with the aldolase-TRAP complex in order to pursue structure-guided optimization of the compound. This work has resulted in the first reported structure of a homologous aldolase from Toxoplasma gondii and identification of a compound that can inhibit sporozoite gliding and invasion.