sentences:  PARPs use a catalytic triad of His-Tyr-Glu to facilitate binding of NAD+ and positioning of the end of the existing poly-ADP ribose chain on the target protein; the Glu facilitates catalysis and formation of a (1->2) O-glycosidic linkage between two ribose molecules.There are several other enzymes that recognize poly-ADP ribose chains, hydrolyse them or form branches; over 800 proteins have been annotated to contain the loosely defined poly ADP-ribose binding motif; therefore, in addition to this modification altering target protein conformation and structure, it may also be used as a tag to recruit other proteins or for regulation of the target protein.Many different amino acid side chains have been described as ADP-ribose acceptors.