K63-polyubiquitinated RIP1 binds to IKBKG (NEMO), resulting in the recruitment of the IKK complex to the receptor complex (Ea CK et al. 2006).

In addition, the linear polyubiquitination has been implicated in the NFkB activation. The linear ubiquitin chain assembly complex (LUBAC) ligase consisting of HOIL-1L, HOIP, and SHARPIN, specifically generates linear polyubiquitin chains (Kirisako T et al. 2006; Walczak H et al. 2012). IKBKG (NEMO), a regulatory component of the IκB kinase (IKK) complex, is a substrate of LUBAC. LUBAC-mediated IKBKG ubiquitination enhances IKBKG interaction with the TNF-alpha receptor signaling complex and stabilizes this protein complex to promote activation of NFkB (Haas TL et al. 2009).

Structural analysis revealed that NPL4 zinc finger 1 (NZF1) of HOIP can simultaneously bind both leucine zipper (CoZi) domains of NEMO (IKBKG) and ubiquitin and that both interactions are involved in the TNF alpha-mediated NFkappaB activation (Fujita H et al. 2014). In addition, NEMO (IKBKG) ubiquitination required RING-between-RING (RBR) domain of HOIL-1L (Smit JJ et al. 2013)