[Show abstract][Hide abstract] ABSTRACT: Protein S-palmitoylation, a hydrophobic post-translational modification, is performed by protein acyltransferases that have a common DHHC Cys-rich domain (DHHC proteins), and provides a regulatory switch for protein membrane association. In this work, we analyzed the presence of DHHC proteins in the protozoa parasite Giardia lamblia and the function of the reversible S-palmitoylation of proteins during parasite differentiation into cyst. Two specific events were observed: encysting cells displayed a larger amount of palmitoylated proteins, and parasites treated with palmitoylation inhibitors produced a reduced number of mature cysts. With bioinformatics tools, we found nine DHHC proteins, potential protein acyltransferases, in the Giardia proteome. These proteins displayed a conserved structure when compared to different organisms and are distributed in different monophyletic clades. Although all Giardia DHHC proteins were found to be present in trophozoites and encysting cells, these proteins showed a different intracellular localization in trophozoites and seemed to be differently involved in the encystation process when they were overexpressed. dhhc transgenic parasites showed a different pattern of cyst wall protein expression and yielded different amounts of mature cysts when they were induced to encyst. Our findings disclosed some important issues regarding the role of DHHC proteins and palmitoylation during Giardia encystation.
[Show abstract][Hide abstract] ABSTRACT: SUMOylation, a posttranslational modification of proteins, has been recently described as vital in eukaryotic cells. In a previous work, we analyzed the role of SUMO protein and the genes encoding the putative enzymes of the SUMOylation pathway in the parasite Giardia lamblia. Although we observed several SUMOylated proteins, only the enzyme Arginine Deiminase (ADI) was confirmed as a SUMOylated substrate. ADI is involved in the survival of the parasite and, besides its role in ATP production, it also catalyzes the modification of arginine residues to citrulline in the cytoplasmic tail of surface proteins. During encystation, however, ADI translocates to the nuclei and downregulates the expression of the Cyst Wall Protein 2 (CWP2). In this work, we made site-specific mutation of the ADI SUMOylation site (Lys101) and observed that transgenic trophozoites did not translocate to the nuclei at the first steps of encystation but shuttled in the nuclei late during this process through classical nuclear localization signals. Inside the nuclei, ADI acts as a peptidylarginine deiminase, being probably involved in the downregulation of CWPs expression and cyst wall formation. Our results strongly indicate that ADI plays a regulatory role during encystation in which posttranslational modifications of proteins are key players.
Biochimica et Biophysica Acta 04/2014; · 4.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Giardia duodenalis causes diarrhoea in humans and a wide range of mammals, including cattle. In cattle, the infection often has a chronic character. Infected calves may excrete cysts for several months, suggesting that Giardia is able to suppress and evade the immune response.
In this study six calves were infected with G. duodenalis assemblage A and E and housed in an environment that allowed reinfection. Cyst excretion was monitored twice a week and blood was collected every two weeks, until decreasing cyst counts indicated the development of protective immunity. The kinetics of the circulating memory cells and serum antibodies were followed up throughout this period. Cyst excretion started 1 week post infection and remained high until week 14. Low cyst counts from week 15 p.i. onwards indicated that the calves had developed immunity.
From week 5 p.i. significant proliferation of CD4+ αβ T-cells was observed after in vitro stimulation with G. duodenalis antigen. Characterisation of the proliferating CD4+ T-cells using real time qPCR showed that at the peak of antigen driven PBMC proliferation the majority of cells were CD4+ T-cells expressing IL-17 and to a lesser extent FoxP3. The cell proliferation was strongly reduced after plastic adhesion of the PBMC, suggesting a role for antigen-presenting cells. Failure to restore proliferation of depleted PBMC with Giardia-stimulated monocyte-derived dendritic cells (MoDC) and unchanged proliferation after depletion of CD21+ B-cells showed that other antigen-presenting cells than MoDC and B-cells were important for T-cell proliferation. Analysis of the antibody response indicated that serum IgG1 and IgA levels against G. duodenalis assemblage A and E increased from week 11 post infection. From the start of the antibody response, all trophozoites stained positive in an immunofluorescence assay with serum antibodies, indicating that a broad repertoire of antibodies was produced against all variant-specific surface proteins.
Further research is necessary to determine which effector T-cell subset produces IL-17 and which cells play a role in antigen presentation.
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