The aspartyl protease plasmepsin V is a very promising antimalarial target

Today’s hottest news is from Nature. Two HHMI groups independently have identified a critical enzyme that allows the malaria-causing parasite, Plasmodium falciparum, to take over and thrive in human red blood cells. As written by the editor, I immediately see the significance of these work ……

A key part of the life cycle of the malaria parasite — and the one that makes transmission via the mosquito to other hosts possible — involves a period of growth inside host red blood cells. During this phase the Plasmodium cells export several hundred proteins into the host blood cell, which they remodel as an environment suitable for parasite multiplication. Proteins destined for export contain a conserved motif called PEXEL, and when this is cleaved in the endoplasmic reticulum the protein can translocate into the host cell. Two independent studies now reveal the identity of the enzyme that cleaves the PEXEL motif as the aspartyl protease plasmepsin V. This finding immediately suggests that plasmepsin V is a potential drug target for antimalarial agents.

Mol Biochem Parasitol. 2008 Aug;160(2):107-15. Epub 2008 May 2.

N-terminal processing of proteins exported by malaria parasites.

Chang HH, Falick AM, Carlton PM, Sedat JW, DeRisi JL, Marletta MA.

Department of Chemistry, University of California, Berkeley, CA 94720, USA.

Malaria parasites utilize a short N-terminal amino acid motif termed the Plasmodium export element (PEXEL) to export an array of proteins to the host erythrocyte during blood stage infection. Using immunoaffinity chromatography and mass spectrometry, insight into this signal-mediated trafficking mechanism was gained by discovering that the PEXEL motif is cleaved and N-acetylated. PfHRPII and PfEMP2 are two soluble proteins exported by Plasmodium falciparum that were demonstrated to undergo PEXEL cleavage and N-acetylation, thus indicating that this N-terminal processing may be general to many exported soluble proteins. It was established that PEXEL processing occurs upstream of the brefeldin A-sensitive trafficking step in the P. falciparum secretory pathway, therefore cleavage and N-acetylation of the PEXEL motif occurs in the endoplasmic reticulum (ER) of the parasite. Furthermore, it was shown that the recognition of the processed N-terminus of exported proteins within the parasitophorous vacuole may be crucial for protein transport to the host erythrocyte. It appears that the PEXEL may be defined as a novel ER peptidase cleavage site and a classical N-acetyltransferase substrate sequence.

PMID: 18534695

Both of these work are based on the paper above published in 2008, where the authors proved that PEXEL (Plasmodium export element) is cleavage and N-acetylated. Now, the enzyme responsible for this cleavage and subsequent dumping has been identified – PMV, the aspartyl protease plasmepsin V.

Here are the papers.

Nature 463, 627-631 (4 February 2010)
DOI: 10.1038/nature08728;
Received 30 July 2009; Accepted 4 December 2009

An aspartyl protease directs malaria effector proteins to the host cell

Justin A. Boddey 1, Anthony N. Hodder 1, Svenja Günther 1, Paul R. Gilson 2, Heather Patsiouras 3, Eugene A. Kapp 3, J. Andrew Pearce 1, Tania F. de Koning-Ward 4, Richard J. Simpson 1,3, Brendan S. Crabb 2 & Alan F. Cowman 1

1 The Walter and Eliza Hall Institute of Medical Research, Melbourne 3052, Australia
2 Macfarlane Burnet Institute for Medical Research and Public Health, Melbourne 3004, Australia
3 Joint Proteomics Facility, Ludwig Institute for Cancer Research, Melbourne 3050, Australia
4 Deakin University, Waurn Ponds 3217, Australia

Correspondence and requests for materials should be addressed to A.F.C. (Email: cowman@wehi.edu.au).

Plasmodium falciparum causes the virulent form of malaria and disease manifestations are linked to growth inside infected erythrocytes. To survive and evade host responses the parasite remodels the erythrocyte by exporting several hundred effector proteins beyond the surrounding parasitophorous vacuole membrane. A feature of exported proteins is a pentameric motif (RxLxE/Q/D) that is a substrate for an unknown protease. Here we show that the protein responsible for cleavage of this motif is plasmepsin V (PMV), an aspartic acid protease located in the endoplasmic reticulum. PMV cleavage reveals the export signal (xE/Q/D) at the amino terminus of cargo proteins. Expression of an identical mature protein with xQ at the N terminus generated by signal peptidase was not exported, demonstrating that PMV activity is essential and linked with other key export events. Identification of the protease responsible for export into erythrocytes provides a novel target for therapeutic intervention against this devastating disease.

Nature 463, 632-636 (4 February 2010)
DOI: 10.1038/nature08726;
Received 30 July 2009; Accepted 7 December 2009

Plasmepsin V licenses Plasmodium proteins for export into the host erythrocyte

Ilaria Russo 1,2, Shalon Babbitt 1,3, Vasant Muralidharan 1,3, Tamira Butler 1, Anna Oksman 1 & Daniel E. Goldberg 1

1 Howard Hughes Medical Institute, Washington University School of Medicine, Departments of Molecular Microbiology and Medicine, St Louis, Missouri 63110, USA
2 Present address: Department of Experimental Medicine and Biochemical Science, University of Perugia, 06126 Perugia, Italy.
3 These authors contributed equally to this work.

Correspondence and requests for materials should be addressed to D.E.G. (Email: Goldberg@borcim.wustl.edu).

During their intraerythrocytic development, malaria parasites export hundreds of proteins to remodel their host cell. Nutrient acquisition, cytoadherence and antigenic variation are among the key virulence functions effected by this erythrocyte takeover. Proteins destined for export are synthesized in the endoplasmic reticulum (ER) and cleaved at a conserved (PEXEL) motif, which allows translocation into the host cell via an ATP-driven translocon called the PTEX complex. We report that plasmepsin V, an ER aspartic protease with distant homology to the mammalian processing enzyme BACE, recognizes the PEXEL motif and cleaves it at the correct site. This enzyme is essential for parasite viability and ER residence is essential for its function. We propose that plasmepsin V is the PEXEL protease and is an attractive enzyme for antimalarial drug development.

By the way, if you have a minute, definitely check out this video about the life cycle of Malaria.