Throwing a chemical spanner in the malaria invasion motor : interaction and dynamics of the Plasmodium MTIP/MyoA complex

• Main Author: Thomas, Jemima Carys
• Other Authors: Tate, Ed
• Published: Imperial College London 2011
• Subjects: 616.9883
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.537216

Malaria kills over one million people per year and has devastating social and economic effects on endemic countries. It is caused by the Plasmodium parasite which has a history of developing resistance to anti-malarial drugs, meaning new therapeutics are urgently required. A key event in the Plasmodium life cycle is the invasion of human erythrocytes. The force for this invasion is derived from an actomyosin motor located inside the parasite plasma membrane. This molecular motor consists of a type XIV myosin, Myosin A (MyoA), bound to myosin tail interacting protein (MTIP). The MTIP/MyoA protein-protein interaction is a potential anti-malarial drug target; disruption of this complex should stall erythrocyte invasion and kill the parasite. In the work discussed in this thesis the MyoA tail was mimicked using short chain peptides for the study of MTIP/MyoA binding in vitro. Development of fluorescence assays for the analysis of MyoA peptide binding to MTIP and the screening of potential inhibitors of this complex is described, together with the application of these assays to identify novel binding motifs at the MTIP/MyoA interface. In combination with peptide arrays, these fluorescence assays were also used to investigate MTIP binding to Myosin B (MyoB), another Plasmodium myosin of unknown function. No binding partners of MyoB have yet been identified in vivo, but results reported here show that MTIP can bind MyoB peptides in vitro. CD spectroscopy and protein NMR experiments were used to investigate the structures of MTIP/MyoA and MTIP/MyoB peptide complexes in solution, and indicate that MTIP undergoes a large conformational change upon myosin peptide binding. These structural techniques together with the fluorescence assays provide a platform for future drug discovery efforts targeting MTIP/MyoA. Finally, the information obtained concerning the MTIP/MyoA interaction was used to design and synthesise α-helix mimetic compounds of MyoA. These compounds were examined for inhibition activity against MTIP/MyoA using fluorescence assays, and appear to be able to disrupt MTIP/MyoA complex formation in vitro. This provides a starting point for future anti-malarial drug development and is a further step towards the chemical validation of MTIP/MyoA as a drug target.