Regulation of A20 and other OTU deubiquitinases by reversible oxidation

Protein ubiquitination is a highly versatile posttranslational modification that regulates as diverse processes as protein degradation and kinase activation. Deubiquitinases hydrolyse ubiquitin modifications from proteins and are hence key regulators of the ubiquitin system. Ovarian Tumour (OTU) deubiquitinases comprise a family of fourteen human enzymes, many of which regulate cellular signalling pathways. OTU deubiquitinases are cysteine proteases that cleave polyubiquitin (polyUb) chains in vitro and in cells, but little is currently known about their regulation. Here we show that OTU deubiquitinases are susceptible to reversible oxidation of the catalytic cysteine residue. High-resolution crystal structures of the catalytic domain of A20 in four different oxidation states reveal that the reversible form of A20 oxidation is a cysteine sulphenic acid intermediate, which is stabilised by the architecture of the catalytic centre. Using chemical tools to detect sulphenic acid intermediates, we show that many OTU deubiquitinases undergo reversible oxidation upon treatment with H(2)O(2), revealing a new mechanism to regulate deubiquitinase activity.