E3 ubiquitin-protein ligase that specifically binds poly-ADP-ribosylated (PARsylated) proteins and mediates their ubiquitination and subsequent degradation. May regulate many important biological processes, such as cell survival and DNA damage response. Acts as an activator of the Wnt signaling pathway by mediating the ubiquitination of PARsylated AXIN1 and AXIN2, 2 key components of the beta-catenin destruction complex. Acts in cooperation with tankyrase proteins (TNKS and TNKS2), which mediate PARsylation of target proteins AXIN1, AXIN2, BLZF1, CASC3, TNKS and TNKS2. Recognizes and binds tankyrase-dependent PARsylated proteins via its WWE domain and mediates their ubiquitination (By similarity). May regulate TNKS and TNKS2 subcellular location, preventing aggregation at a centrosomal location. Neuroprotective protein. Protects the brain against N-methyl-D-aspartate (NMDA) receptor-mediated glutamate excitotoxicity and ischemia, by interfering with PAR-induced cell death, called parthanatos. Prevents nuclear translocation of AIFM1 in a PAR-binding dependent manner. Does not affect PARP1 activation (By similarity). Protects against cell death induced by DNA damaging agents, such as N-methyl-N-nitro-N-nitrosoguanidine (MNNG) and rescues cells from G1 arrest. Promotes cell survival after gamma-irradiation. Facilitates DNA repair. Neuroprotective protein. Protects the brain against N-methyl-D-aspartate (NMDA) receptor-mediated glutamate excitotoxicity and ischemia, by interfering with PAR-induced cell death, called parthanatos. Prevents nuclear translocation of AIFM1 in a PAR-binding dependent manner. Does not affect PARP1 activation. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Can form homooligomers. Interacts with PARsylated AXIN1, AXIN2, BLZF1, CASC3, H1-2, IPO7, LIG3, NCL, PARP1, XRCC1, XRCC5 and XRCC6. Interacts with DDB1, DHX15, IQGAP1, LRPPRC, PARP2, PRKDC, RUVBL2, TNKS1 and TNKS2. Binding often leads to interactor ubiquitination, in the presence of the appropriate E1 and E2 enzymes, and proteasomal degradation. Translocates to the nucleus after DNA damage, such as laser-induced DNA breaks, and concentrates at DNA breaks. This translocation requires PARP1 activation and PAR-binding (By similarity). Expressed at relatively high levels in the brain. Also present in spleen, heart, kidney, testis and liver. In the brain, expressed in the cerebellum, hippocampus, striatum, cortex, frontal cortex and, at lowest levels, in olfactory bulb (at protein level). Predominantly expressed in neurons. Up-regulated in cortical neurons by treatment with N-methyl-D-aspartate (NMDA). Toxic doses of NMDA fail to induce Iduna expression. Sublethal exposure to oxygen-glucose deprivation also induces Iduna protein expression. Also induced by treatments that result in resistance to subsequent ischemic injury, such as 5 minute bilateral common carotid artery occlusion (at protein level). The WWE domain mediates non-covalent PAR-binding. Ubiquitinated; autoubiquitinated. Autoubiquitination is enhanced upon PAR-binding (By similarity). Was named Iduna after the Norse goddess of protection and eternal youth.