Crystal Structure of Pro-plasmepsin II from Plasmodium falciparum. Nina Khazanovich1, Maia M.Chernaia1, Robert G. Ridley2 , Michael N.G. James1, 1MRC Group in Protein Structure and Function, Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada, T6G 2H7, and 2F. Hoffmann-La Roche, CH-4070, Basel, Switzerland
In the course of a malaria infection, the parasite Plasmodium falciparum digests its human host's haemoglobin in an acidic compartment called the digestive vacuole. P. falciparum utilises three enzymes to degrade haemoglobin: the homologous aspartic proteinases, plasmepsin I and plasmepsin II, and a cysteine proteinase. Like all known parasitic and mammalian aspartic proteinases, the plasmepsins are initially produced as zymogens, inactive precursors with an amino-terminal extension or pro-segment. In the acidic environment of the digestive vacuole, the zymogens are converted to the mature enzymes. While the mature plasmepsins exhibit sequence similarity to other aspartic proteinases such as renin and cathepsin D, their pro-segments are unique in size and sequence among the zymogens. In addition, the plasmepsin pro-segments contain a putative trans-membrane helix, a feature not found in any other aspartic proteinase zymogen.
The plasmepsins are interesting from a pharmaceutical perspective as targets for anti-malarial drug design. Malaria affects 300 million people every year, and the alarming rise in resistance to traditionally used anti-malarial drugs has necessitated the search for new strategies for combatting this disease. Currently the search is on for drugs which inhibit plasmepsin I and II. However, as we learn more about the activation of pro-plasmepsins, this process may prove to be a valuable drug-design target.
We have determined the crystal structure of recombinant pro-plasmepsin II, where the 125-residue pro-segment has been truncated to 48 amino-acids. The protein is inactive, but auto-activates at acidic conditions. Pro-plasmepsin II was crystallized in space group P1 (a = 52.0Å, b = 84.0Å, c = 98.4Å, a = 98.5[ring], [beta] = 97.1[ring], [gamma] = 106.2[ring]) with four molecules in the asymmetric unit. Details of the structure will be presented.