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.
Highlights
The flagellated protozoan parasite Giardia lamblia is a major cause of non-viral/non-bacterial diarrheal disease worldwide
When Giardia encysting cells were analyzed, the assay displayed a larger amount of palmitoylated proteins, as can be judged by the larger number of bands displayed compared to trophozoites (Figure 1A, encysting trophozoites (ET)/hyd2)
The four bands (169, 66, 42, and 21 kDa) were observed for High Cysteine Non-variant Cyst protein (HCNCp) ET purified sample compared to the control, showing that the full length and the smaller epitope-tagged fragments of the HCNCp protein were palmitoylated in encysting parasites (Figure 1B, HCNCp ET/hyd+)
Summary
The flagellated protozoan parasite Giardia lamblia is a major cause of non-viral/non-bacterial diarrheal disease worldwide. This parasite can cause asymptomatic colonization or acute or chronic diarrheal illness and malabsorption [1]. The inverse process is called encystation and begins when the trophozoites migrate to the lower part of the small intestine where they receive signals that trigger synthesis of the components of the cyst wall. Several other proteins, whose roles in encystation are yet to be discovered, are upregulated at the transcriptional level [2], [3]. There is some evidence of the role of PTM in gene regulation for the control of this process [9]
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