Location: Animal Parasitic Diseases
Title: Global proteomic analysis of the oocyst/sporozoite of Toxoplasma gondii reveals commitment to a host-independent lifestyle Authors
Submitted to: Biomed Central (BMC) Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 12, 2012
Publication Date: March 1, 2013
Citation: Possenti, A., Fratini, F., Pizzi, E., Fantozzi, L., Pozio, E., Dubey, J.P., Ponzi, M., Spano, F. 2013. Global proteomic analysis of the oocyst/sporozoite of Toxoplasma gondii reveals commitment to a host-independent lifestyle. Biomed Central (BMC) Genomics. 14:183. Interpretive Summary: Toxoplasma gondii is a single-celled parasite of all warm-blooded hosts worldwide. It causes mental retardation and loss of vision in children, and abortion in livestock. Cats are the main reservoir of T. gondii because they are the only hosts that can excrete the resistant stage (oocyst) of the parasite in the feces. Humans become infected by eating under-cooked meat from infected animals, as well as food and water contaminated with oocysts. The chemical basis of oocyst resistance is unknown. The authors report biochemical make up of the oocyst. The results will be of interest to biologists, and parasitologists.
Technical Abstract: Human toxoplasmosis is caused by the coccidian parasite Toxoplasma gondii and can be acquired either congenitally or via the oral route. In the latter case, transmission is vehicolated by two distinct invasive stages, i.e., bradyzoites contained in tissue cysts or sporozoites enveloped in environmentally resistant oocysts shed by felids in their feces. The central epidemiological role played by the oocyst of T. gondii and the limited knowledge on its expressed proteome prompted us to undertake a global proteomic survey of this parasite stage, using one-dimensional gel electrophoresis coupled to liquid chromatography-linked tandem mass spectrometry. The analysis of total or fractionated protein extracts obtained from partially sporulated oocysts of the T. gondii strain VEG (genotype III) yielded a dataset of 1685 non reduntant proteins, accounting for ~21% of the total predicted proteome. Approximately 35% of the identifications corresponded to hypothetical proteins, whereas 54% were classified according to the MIPS functional catalogue database. Importantly, the comparison of the VEG oocyst dataset with the extensively covered proteome of the T. gondii tachyzoite identified 211 putative oocyst/sporozoite-specific proteins (POSP), some of which were validated by Western blot analysis of oocyst and tachyzoite lysates. The functional profile of the POSP subset is consistent with the adaptation of T. gondii oocysts to the nutrient-poor and stressing extracellular environment, as shown by the preponderance of enzymes involved in metabolism (33) and energy production (12) or by the presence of a photolyase DNA repair enzyme. In particular, proteomic data showed that, compared to tachyzoites, oocysts have a greater capability of de novo amino acid biosynthesis and are well equipped to fuel the Krebs cycle with the acetyl-CoA generated through the '-oxidation of fatty acids and the degradation of branched amino acids. In addition, our data indicated that T. gondii sporozoites and tachyzoites possess extensively overlapping repertoires of invasion-related proteins, yet sporozoites express a broader complement of proteins involved in the formation of the moving junction, including paralogs of the mutually interacting AMA1 and RON2 molecules. Finally, the comparison between proteomic and microarray data showed that the stage-specific expression of a significant fraction of the POSPs does not correlate with different mRNA levels in oocysts and tachyzoites, suggesting the existence of post-transcriptional control mechanisms.