ABSTRACT
Toxoplasma gondii is an obligate intracellular parasite and the causative agent of toxoplasmosis. Protein palmitoylation is known to play roles in signal transduction and in enhancing the hydrophobicity of proteins thus contributing to their membrane association. Global inhibition of protein palmitoylation has been shown to affect T. gondii physiology and invasion of the host cell. However, the proteins affected by this modification have been understudied. This paper shows that the small heat shock protein 20 from T. gondii (TgHSP20) is synthesized as a mature protein in the cytosol and is palmitoylated in three cysteine residues. However, its localization at the inner membrane complex (IMC) is dependent only on N-terminal palmitoylation. Absence or incomplete N-terminal palmitoylation causes TgHSP20 to partially accumulate in a membranous structure. Interestingly, TgHSP20 palmitoylation is not responsible for its interaction with the daughter cells IMCs. Together, our data describe the importance of palmitoylation in protein targeting to the IMC in T. gondii.
Subject(s)
Fibroblasts/metabolism , HSP20 Heat-Shock Proteins/metabolism , Intracellular Membranes/metabolism , Lipoylation , Toxoplasma/metabolism , Toxoplasmosis/parasitology , Blotting, Western , Cells, Cultured , Cysteine/chemistry , Cysteine/genetics , Cysteine/metabolism , Cytosol/metabolism , Fibroblasts/cytology , Fluorescent Antibody Technique , HSP20 Heat-Shock Proteins/genetics , Humans , Immunoprecipitation , Mutation/genetics , Protein Transport , Signal Transduction , Toxoplasma/growth & development , Toxoplasmosis/metabolismABSTRACT
Protein palmitoylation is the reversible covalent attachment of palmitic acid onto proteins. This post-translational modification has been shown to play a part in diverse processes such as signal transduction, cellular localization and regulation of protein activity. Although many aspects of protein palmitoylation have been identified in mammalian and yeast cells, little is known of this modification in Toxoplasma gondii. In order to determine the functional role of protein palmitoylation in T. gondii, tachyzoites were treated with the palmitoylation inhibitor 2-bromopalmitate (2-BP). Parasites treated with 2-BP displayed a significant increase in non-circular trails which were longer than those trails left by non-treated parasites. Furthermore, 2-BP treatment reduced the invasion process to the host cells. Long-term treatment of intracellular tachyzoites resulted in major changes in parasite morphology and shape in a dose-dependent manner. These results suggest that palmitoylation could be modifying proteins that are key players in gliding, invasion and cytoskeletal proteins in T. gondii.
