This protein modification is produced by ADP-ribosyltransferase enzymes, which transfer the ADP-ribose group from nicotinamide adenine dinucleotide (NAD+) onto acceptors such as arginine, glutamic acid or aspartic acid residues in their substrate protein. In humans, one type of ADP-ribosyltransferases are the NAD:arginine ADP-ribosyltransferases, which modify amino acid residues in proteins such as histones by adding a single ADP-ribose group.[5] These reactions are reversible; for example, when arginine is modified, the ADP-ribosylarginine produced can be removed by ADP-ribosylarginine hydrolases.[6]
ADP-ribose can also be transferred to proteins in long branched chains, in a reaction called poly(ADP-ribosyl)ation.[7] This protein modification is carried out by the poly ADP-ribose polymerases (PARPs) which are found in most eukaryotes, but not prokaryotes or yeast.[7][8] The poly(ADP-ribose) structure is involved in the regulation of several cellular events and is most important in the cell nucleus, in processes such as DNA repair and telomere maintenance.[8]
Bacterial toxins
ADP-ribosylation is also responsible for the actions of some bacterial toxins, such as cholera toxin and pertussis toxin. These toxin proteins are ADP-ribosyltransferases that modify target proteins in human cells. For example, cholera toxin ADP-ribosylates G proteins, which causes massive fluid secretion from the lining of the small intestine and results in life-threatening diarrhea.[9]
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