Upon stimulation by pathogen-associated inflammatory signals, TANK-binding kinase 1 (TBK1) and inhibitor of ?B kinase epsilon (IKKi) induce type I interferon expression and modulate nuclear factor ?B (NFkB) signaling (Fitzgerald KA et al. 2003; Hemmi H et al. 2004). The structural studies of TBK1 revealed a dimeric assembly which is mediated by several interfaces involving kinase domain (KD), a ubiquitin-like domain (ULD), and an alpha-helical scaffold dimerization domain (SDD) of TBK1 (Larabi A et al. 2013; Tu D et al. 2013). ULD of TBK1 and IKKi was involved in the control of kinase activation, substrate presentation and downstream signaling (Ikeda F et al 2007; Tu D et al. 2013). An intact TBK1 dimer was a subject to K63-linked polyubiquitination on lysines 30 and 401 (Tu D et al. 2013). Activation of TBK1 rearranged the KD into an active conformation while maintaining the overall dimer conformation (Larabi A et al. 2013). The ubiquitination sites and dimer contacts are conserved in the close homolog IKKi (Tu D et al. 2013). The activation of TBK1 and IKKi may occur through autophosphorylation or via activity of a distinct protein kinase (Clark et al. 2009). Other studies demonstrated an essential role of TRAF3 in the activation of TBK1 (Hacker et al 2006). TBK1 and IKKi were found to interact with scaffold proteins TANK (TRAF family member associated NFkB activator), NAP1 (NAK-associated protein 1), SINTBAD (similar to NAP1 TBK1 adaptor) which connect TBK1/IKKi to pathogen-activated signaling cascades (Pomerantz JL and Baltimore D 1999; Guo B and Cheng G 2007; Gatot JC et al. 2007; Ryzhakov G and Randow F 2007; Goncalves A et al. 2011).
Chicken IKK epsilon protein, confirmed by transcript evidedence, shows 68% amino acid sequence identity to its human ortholog.