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Characterization of Calcium Signaling Proteins in Toxoplasma Gondii

Arrizabalaga, Gustavo
Indiana University-Purdue University Indianapolis
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Toxoplasma gondii is an obligate intracellular parasite known to chronically infect a third of the world's human population. T. gondii infections can lead to severe disease and death in immuno-compromised individuals and significant birth defects when acquired in utero. T. gondii depends on its ability to move into and out of cells to survive and propagate within an infected host. Events required for T. gondii invasion, egress and motility are regulated by calcium signaling processes that include proteins and factors significantly divergent from those of the human host. Thus, inhibition of the calcium signaling pathways that control essential events like invasion and egress constitutes a realistic method to combat this pathogen. Such a strategy requires a better understanding of T. gondii's calcium signaling and accordingly we have taken a forward genetic approach to the identification of calcium signaling proteins.

In the last decade we have isolated various mutants with defective responses to artificially induced calcium fluxes. Phenotypic analysis of these mutants has allowed us to learn about various steps leading to the initiation of motility in response to calciu fluxes. Nonetheless, our understanding of these strains and calcium signaling is incomplete, as we have, until recently, been unable to identify the affected genes. The fast pace of development of sequencing techniques has made whole genome sequencing accessible to individual laboratories and thus we have begun revisiting these orphan T. gondii mutants. We have shown the strength of this approach, as well as our ability to harness it, in identifying a mutation in a calcium dependent protein kinase (TgCDPK3) as the cause of the phenotypes in one of these mutants.

Currently, two mutants with distinct calcium signaling related phenotypes remain molecularly uncharacterized. Building on our recent success using whole genome sequencing, we propose to sequence the remaining mutants as to identify and begin functional characterization of proteins involved in calcium signaling in T. gondii. Since this study is exploratory and focuses on further analysis of an existing data set, it is ideal for the RO3 fundin mechanism.

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Public Health Relevance:
One of the most widespread protozoan parasites, Toxoplasma gondii, can lead to severe disease and even death on immunocompromised individuals as well as in the developing fetus. It is the focus of our work to identify the protein involved in signaling the initiation of movement in this parasite. Since inhibiting motility would control this opportunistic infection, our work will lead to the discovery of new drug targets and therapies to combat toxoplasmosis.
Funding Source
Nat'l. Inst. of Allergy and Infectious Diseases
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Bacterial Pathogens
Microbiological Standards and Guidelines