Determining Turnover Rates of Proteins That Perform Different Functions During the Parasite Lytic Cycle in Toxoplasma gondii

Abstract

Toxoplasma gondii is an obligate, intracellular, protozoan parasite that infects approximately one third to half of the world’s population. This apicomplexan parasite is the causative agent for toxoplasmosis, the clinical manifestation of T. gondii. Due to the importance of proteins as metabolic regulators, the amount of protein being produced and degraded in any organism is important. Monahan found that although the protein synthesis inhibitor anisomycin was highly effective in reducing global protein rates of T. gondii, the parasite was still able to invade in the presence of anisomycin. This suggests that the rate at which proteins are turned over may be dependent on the role they serve. The results of this research assessed that the temporal regulation of invasion linked protein expression differs from that of other proteins, that perhaps invasion linked proteins have a lower turnover rate compared to non-invasion linked proteins. To measure the turnover rate, we added a protein synthesis inhibitor, thereby allowing us to measure the degradation rate indirectly. We found that amount of protein decay is best modeled by an exponential model. Therefore, we coined a new figure, normalized turnover rate to reflect the underlying biology rather than amount of protein or time. After applying the Tukey test, we found that the normalized turnover rate of invasion linked (GRA2, GRA3) proteins is lower than that of non-invasion linked. Assessing rates of protein turnover is critical in understanding the biology of the parasite T. gondii as it allows for a potential therapeutic target for invasion linked proteins, allowing future research towards mitigating parasitic infection.