Macrodomains are found in a variety of proteins with diverse cellular functions, as a stand-alone domain or in combination with other domains like in histone macroH2A and some PARPs (poly ADP-ribose polymerases). Macrodomains can recognize ADP-ribose (ADPr) in both its free and protein-linked forms, in related ligands, such as O-acyl-ADP-ribose (OAADPr), and even in ligands unrelated to ADPr. This family includes eukaryotic macrodomain proteins such as human MacroD1 and MacroD2, and bacterial proteins such as Escherichia coli YmdB; these have been shown to be O-acetyl-ADP-ribose (OAADPr) deacetylases that efficiently catalyze the hydrolysis of OAADPr to produce ADP-ribose and free acetate. OAADPr is a sirtuin reaction product generated from the NAD+-dependent protein deacetylation reactions and has been implicated as a signaling molecule. By acting on mono-ADP-ribosylated substrates, OAADPr deacetylases may reverse cellular ADP-ribosylation.
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