GlSir2.1 of Giardia lamblia is a NAD+-dependent cytoplasmic deacetylase

The sirtuins are a group of well-conserved proteins widely distributed across all domains of life. These proteins are clustered in the class III of histone deacetylases and are distinctly characterized by their dependence upon NAD+ to carry out the deacetylation of lysine residues in histone proteins (H3 and H4) and non-histones such as the transcription factor p53. The requirement of NAD+ for sirtuin activity makes this group of proteins metabolic sensors, which are favored during caloric stress. Currently, it is known that these proteins are involved in numerous cellular processes that are fundamental for the proper functioning of cells, including control of the cell cycle and cellular survival. In spite of the importance of sirtuins in cell functions, the role that these proteins play in protozoan parasites is not completely understood. In this study, bioinformatic modeling and experimental characterization of the candidate G1Sir2.1 present in the genome of Giardia lamblia were carried out. Consequently, cloning, expression, purification, and in vitro evaluation of the recombinant GlSir2.1 protein's capacity for deacetylation were performed. This allowed for the identification of the NAD+-dependent deacetylase activity of the identified candidate. Production of anti-rHis-GlSir2.1 polyclonal antibodies enabled the observation of a cytoplasmic localization for the endogenous protein in trophozoites, which exhibited a perinuclear aggregation and co-localization with acetylated cytoskeleton structures such as the flagella and median body. Currently, GlSir2.1 is the second sirtuin family member identified in G. lambia, with a demonstrated cytoplasmic localization in the parasite.