Entamoeba Shows Reversible Variation in Ploidy under Different Growth Conditions and between Life Cycle Phases

Abstract

We have discovered four sirtuin genes in Entamoeba histolytica, two of which are similar to eukaryotic sirtuins and two to bacterial and archaeal sirtuins. The eukaryotic sirtuin homolog, EhSir2a showed NAD+ dependent deacetylase activity and was sensitive to Class III HDAC inhibitors. Localization of EhSir2a at different cellular sites suggested that this deacetylase could have multiple targets. Using an E. histolytica cDNA library in the yeast two-hybrid genetic screen, we identified several proteins that bound to EhSir2a. These proteins included Eh α-tubulin, whose interaction with EhSir2a was validated in E. histolytica. We have shown that EhSir2a deacetylated tubulin and localised with microtubules in E. histolytica. Increased expression levels of EhSir2a in stable transformants led to reduced number of microtubular assemblies in serum synchronised cells. This effect was abrogated by mutations in the deacetylase domain of EhSir2a, showing that EhSir2a deacetylase activity affected the stability and number of microtubular assemblies during the cell cycle of E. histolytica. Our results suggest that epigenetic modification of tubulin by EhSir2a is one of the mechanisms that regulates microtubular assembly in E. histolytica.