Poster Presentation RACI Biomolecular Division Conference 2013

The design of small molecule inhibitors of Plasmepsin V for intervention against malaria (#66)

Michelle Gazdik 1 2 , Brad Sleebs 1 2 , Alan Cowman 1 2 , Justin Boddey 1 2
  1. Medical Biology, The University of Melbourne, Parkville, VIC, Australia
  2. Chemical Biology/Infection and Immunity, Walter and Eliza Hall Institute, Parkville, VIC, Australia

The human malaria parasite Plasmodium falciparum is responsible for the most severe form of malaria. Central to the capacity of this organism to grow inside red blood cells and thrive inside the blood-stream is its ability to export an estimated 450 proteins into the host cell erythrocyte. The proteins exported to the erythrocyte possess a conserved N-terminal export motif termed the Plasmodium export element (PEXEL). In order for proteins to be exported, the PEXEL motif (RxLxE/Q/D) must be cleaved by an ER-resident aspartic protease called Plasmepsin V (PMV).1-4 PMV is one of ten malarial Plasmepsins and is expressed in the blood, gametocyte and liver stages of the parasite life cycle.  It is hypothesized that a small inhibitor of PMV would block the export of essential proteins into the host cell, resulting in parasite death. Hence, PMV is considered a prime target for the development of new antimalarial therapies.

The goal of this project is to design small molecule inhibitors of PMV that block protein export in parasites. A common practice of targeting aspartic proteases involves the use of transition state (TS) mimetics. Statine is one of many TS mimetics successfully used to inhibit aspartyl proteases whereby it mimics the tetrahedral state of peptide-bond hydrolysis. A series of compounds were synthesised and the most potent compounds were shown to inhibit PMV with an IC50 of 20 nM. However, these compounds only exhibit moderate activity in parasite cultures. We aim to enhance the potency of the mimetics in parasite culture by improving membrane permeability and proteolytic stability. One strategy to improve these properties is via the N-methylation of the peptide backbone. Another strategy involves altering the P3 region of the mimetic, housing the polar guanidine moiety of arginine. The synthesis of analogues and the outcome of thesestrategies are discussed.

  1. Boddey, J. A.; Hodder, A. N.; Gunther, S.; Gilson, P. R.; Patsiouras, H.; Kapp, E. A.; Pearce, J. A.; de Koning-Ward, T. F.; Simpson, R. J.; Crabb, B. S.; Cowman, A. F. An aspartyl protease directs malaria effector proteins to the host cell. Nature 2010, 463, 627-631.
  2. Chang, H. H.; Falick, A. M.; Carlton, P. M.; Sedat, J. W.; DeRisi, J. L.; Marletta, M. A. N-terminal processing of proteins exported by malaria parasites. Molecular & Biochemical Parasitology 2008, 160, 107-15.
  3. Boddey, J. A.; Moritz, R. L.; Simpson, R. J.; Cowman, A. F. Role of the Plasmodium export element in trafficking parasite proteins to the infected erythrocyte. Traffic 2009, 10, 285-299.
  4. Russo, I.; Babbitt, S.; Muralidharan, V.; Butler, T.; Oksman, A.; Goldberg, D. E. Plasmepsin V licenses Plasmodium proteins for export into the host erythrocyte. Nature 2010, 463, 632-636.