This is a PUB domain (PNGase/UBA- or UBX-containing domain), found in E3 ubiquitin-protein ligase RNF31, also known as Ring finger protein 31 and HOIL-1-interacting protein (HOIP) (EC:2.3.2.27) [1]. RNF31/HOIP is observed to contribute to inborn human immunity disorders, in which RNF31/HOIP missense mutation at PUB domain gives rise to the de-stabilized LUBAC complex (linear ubiquitin chain assembly complex) and subsequently causes the auto-inflammation and immunodeficiency. In addition, RNF31 is reported to modify ERK and JNK pathways leading to cisplatin resistance [2]. Functional studies indicate that HOIP and OTULIN interact and act as a bimolecular editing pair for linear ubiquitin signals where the HOIP-PUB domain binds to the PUB interacting motif (PIM) of OTULIN and the chaperone VCP/p9. This interaction plays an important role where the HOIP binding to OTULIN is required for the recruitment of OTULIN to the TNF receptor complex and to counteract HOIP-dependent activation of the NF-KB pathway [3 , 4].

1: RBR E3 ubiquitin ligases: new structures, new insights, new questions. Spratt DE, Walden H, Shaw GS; Biochem J. 2014;458:421-437. PMID:24576094

2: Atypical ubiquitin ligase RNF31: the nuclear factor modulator in breast cancer progression. Zhu J, Zhuang T, Yang H, Li X, Liu H, Wang H; BMC Cancer. 2016;16:538. PMID:27460922

3: Binding of OTULIN to the PUB domain of HOIP controls NF-kappaB signaling. Schaeffer V, Akutsu M, Olma MH, Gomes LC, Kawasaki M, Dikic I; Mol Cell. 2014;54:349-361. PMID:24726327

4: Molecular basis and regulation of OTULIN-LUBAC interaction. Elliott PR, Nielsen SV, Marco-Casanova P, Fiil BK, Keusekotten K, Mailand N, Freund SM, Gyrd-Hansen M, Komander D; Mol Cell. 2014;54:335-348. PMID:24726323