We are interested in the cell and molecular biology of protozoan parasites. Most of our work is focused on members of the phylum Apicomplexa. Organisms in this group cause a number of important diseases including malaria, severe opportunistic infections associated with AIDS, and fetal and early childhood diseases. We use a broad array of modern genomic, genetic, cell biological and biochemical approaches to understand fundamental parasite biology and use this knowledge to identify and develop targets for intervention. Currently we are focusing on the following specific areas:
The function and cell biology of the parasite chloroplast
Apicomplexan parasites harbor a remnant chloroplast (the apicoplast) that they obtained through secondary endosymbiosis. This organelle is essential for parasite growth and as human cells lack chloroplasts offers a unique opportunity for anti-parasitic drug development. Using Toxoplasma gondii as a robust genetic model we are characterizing the specific metabolic functions of the organelle to pinpoint which pathway(s) would be most suitable as a drug target. The apicoplast also provides a tractable model to study the cell biology of endosymbiosis. What is the cellular machinery that builds, maintains and replicates an organelle that formed through the merger of three previously independent organisms (one prokaryotes and two eukaryotes)? Our current work uses a mix of genomics and genetics to mechanistically dissect apicoplast biogenesis, protein import and division.
Novel targets for the treatment of Cryptosporidiosis
Cryptosporidium is an important human pathogen causing severe disease in AIDS patients and young children. Neither vaccines nor fully effective drugs are available for this disease. We are studying the nucleotide metabolism ofCryptosporidium parvum in an effort to develop effective therapy. We have discovered that the parasite depends entirely on salvage of purines and pyrimidines from its host cell and that several key enzymes were obtained via horizontal gene transfer from a bacterial source. Current work is focused on the further development of lead compounds obtained through a completed high throughput screen in collaboration with the Hedstrom lab at Brandeis. Taking a broader biological perspective we are also interested to learn what the selective advantages might been that have fixed these bacterial genes in the parasite’s eukaryotic genome.
Forward genetic analysis in Toxoplasma gondii
Forward genetic analysis by mutant isolation and complementation is a powerful approach to dissect pathogen biology. Over the last years we have developed a number of strategies and reagents to push this technology forward. We have isolated temperature sensitive mutants using a fluorescent parasite line in a high throughput replica assay. To identify the genes affected in these mutants we have developed an expression cloning system for phenotypic complementation . In addition we have also used this system for expression cloning using antibodies and GFP localization as screens.
- Sheiner, L., Fellows, J.D., Brooks, C.F., Agrawal, S., Holmes, Z.C., Bietz, I., Flinner, N., Heiny, S., Mirus, O., Przyborski, J.M. and Striepen, B. (2015) Toxoplasma gondii Toc75 functions in import of luminal but not peripheral apicoplast proteins. Traffic. In press.
- Vinayak, S.*, Pawlowic, M.C.*, Sateriale, A*, Brooks, C.F., Studstill, J.C., Bar-Peled, Y., Cirpriano, M.J. and Striepen, B. (2015) Genetic modification of the diarrheal pathogen Cryptosporidium parvum. Nature 253:477-480 (*equal contribution).
- Francia, M.E., and Striepen B. (2014) Cell division mechanisms of apicomplexan parasites, Nature Reviews Microbiology 12:125-136.
- Striepen, B. (2013) Time to tackle cryptosporidiosis, Nature 503: 189-191van Dooren, G.G. and Striepen B. (2013) The algal past and parasite present of the apicoplast. Annu Rev. Microbiol 67: 271–289.
- Francia, M.E., Jordan, C.N., Patel, J., Sheiner, L., Demerely, J.L., Fellows, J.D., deLeon, J., Morrissette, N.S., Dubremetz, J.F., and Striepen, B. (2012) Cell division in apicomplexan parasites is organized by a homolog of the striated rootlet fiber of algal flagella. PLoS Biology,10:e1001444. (cover)
- Ramarkrishnan, S., Docampo, M.D., Macrae, J.I., Pujol, F., Brooks, C.F., van Dooren, G.G., Hiltunen, J.K., Kastaniatos, A, McConville, M.J., and Striepen, B. (2012) The apicoplast and endoplasmic reticulum cooperate in fatty acid biosynthesis in the apicomplexan parasite Toxoplasma gondii, J. Biol. Chem., 287: 4957-4971.
- Sheiner, L., Demerely, J., Poulson, S., Michael Benke, White, Michael and Striepen, B. (2011) A systematic screen to discovery and analyze apicoplast proteins identifies a conserved and essential protein import factor. PLoS Pathogens, 7: e1002392.
- Nair, S.C., Brooks, C.F., Goodman, C.D, Sturm, A., McFadden,G.I., Sndriyal, S., Anglin, J.L, Song, Y., Moreno, N.J., and Striepen, B. (2011) Apicoplast isoprenoid precursor synthesis and the molecular basis of fosmidomycin resistance in Toxoplasma. J. Exp. Med. 208: 1547-1559.
- Brooks, C.F., Francia, M.E., Gissot, M. Croken, M.M., Kim, K., and Striepen, B. (2011) Toxoplasma gondii sequesters centromeres to a specific nuclear region throughout the cell cycle. Proc. Natl. Acad. Sci. 108: 3767-3772.
- Sharling, L, Liu, X., Gollapalli D.R., Maurya S. K. Hedstrom, L., Striepen, B. (2010) A screening pipeline for antiparasitic agents targeting Cryptosporidium inosine monophosphate dehydrogenase. PLoS Negl. Trop. Dis. 10: e794.
- Brooks, C.F., Johnsen, H., van Dooren, G.G., Muthalagi, M., Liu, S.S., Bohne, W., Fischer, K., Striepen B. (2010) The Toxoplasma Apicoplast Phosphate Translocator Links Cytosolic and Apicoplast Metabolism and Is Essential for Parasite Survival. Cell Host & Microbe: 7(1):62-73.
- Agrawal, S., van Dooren, G.G., Beatty, W.L., Striepen, B. (2009) Genetic evidence that an endosymbiont-derived ERAD system functions in import of apicoplast proteins. J. Biol. Chem. 284:33683-33691.
- van Dooren, G.G., Reiff, S, Tomova, C., Meissner, M., S., Humbel, B., M., and Striepen, B. (2009) A novel dynamin-related protein has been recruited for apicoplast fission in Toxoplasma gondii. Curr. Biol. 19: 267-276.
- van Dooren, G.G., Tomova, C., Agrawal, S., Humbel, B., and Striepen, B. (2008) Toxoplasma gondii Tic20 is essential for apicoplast protein import. Proc. Natl. Acad. Sci. USA 105:13574-13579.
- Umejiego, N.N., Gollapalli, D., Sharling, L., Volftsun, A., Lu, J., Stroupe, A.H.,Benjamin, N., Striepen, B. and Hedstrom, L. (2008) Targeting a prokaryotic protein in a eukaryotic pathogen: identification of lead compounds against Cryptosporidiosis. Chemistry & Biology 15: 70-77.
- Gubbels, M.J., Lehmann, M., Muthalagi, M., Jerome, M.E., Brooks, C., Szatanek, T. Flynn, J., Parrot, B., Radke, J., Striepen, B. * and White, M.W. * (2008) Forward genetic analysis of the apicomplexan cell division cycle in Toxoplasma gondii. PLoS Pathogens 4: E36.(*joint senior authors)
- Striepen, B., Jordan, C.N., Reiff, S. and van Dooren, G.G. (2007) Building the perfect parasite: apicomplexan cell division. PLoS Pathogens 3: e78
- Mazumdar, J., Wilson, E., Masek, K., Hunter, C. and Striepen, B (2006) Apicoplast fatty acid synthesis is essential for organelle biogenesis and survival in Toxoplasma gondii. Proc. Natl. Acad. Sci. 103:13192-13197.