Dimerization and Ubiquitin Mediated Recruitment of A20, a Complex Deubiquitinating Enzyme

A20 is an anti-inflammatory protein linked to multiple human autoimmune diseases and lymphomas. A20 possesses a deubiquitinating motif and a zinc finger, ZF4, that binds ubiquitin and supports its E3 ubiquitin ligase activity. To understand how these activities mediate A20's physiological functions, we generated two lines of gene-targeted mice, abrogating either A20's deubiquitinating activity (Tnfaip3^OTU mice) or A20's ZF4 (Tnfaip3^ZF4 mice). Both Tnfaip3^OTU and Tnfaip3^ZF4 mice exhibited increased responses to TNF and sensitivity to colitis. A20's C103 deubiquitinating motif restricted both K48- and K63-linked ubiquitination of receptor interacting protein 1 (RIP1). A20's ZF4 was required for recruiting A20 toubiquitinated RIP1. A20^OTU proteins and A20^ZF4 proteins complemented each other to regulate RIP1 ubiquitination and NFκB signaling normally in compound mutant Tnfaip3^OTU/ZF4 cells. This complementation involved homodimerization of A20 proteins, and we have defined an extensive dimerization interface in A20. These studies reveal how A20 proteins collaborate to restrict TNF signaling. •A20's ZF4 motif binds ubiquitin and mediates recruitment to ubiquitinated RIP1•A20's C103 deubiquitinating motif restricts both K48 and K63 ubiquitination of RIP1•A20C103 and A20ZF4 mutant proteins complement each other invivo•A20 proteins dimerize invitro and invivo via a novel interface.