This is the ubiquitin-like domain (ULD) found in TANK-binding kinase 1 (TBK1). TBK1 is a serine/threonine kinase and a noncanonical member of the IKK family implicated in diverse cellular functions, including innate immune response as well as tumorigenesis and development [1]. It has been reported that the ULD of TBK1 regulates kinase activity, playing an important role in signaling and mediating interactions with other molecules in the IFN pathway. Deletion of ULD indicates that it is required for the kinase domain to form an enzymatically active conformation. TBK1 ULD has a ubiquitin-like structure and an Ile44 hydrophobic patch, which is conserved among ULDs and IKK and IKK-related proteins. This hydrophobic patch is involved in ULD-SDD interactions in TBK1 and other IKK and IKK-related proteins [2].

1: TBK1: a new player in ALS linking autophagy and neuroinflammation. Oakes JA, Davies MC, Collins MO; Mol Brain. 2017;10:5. PMID:28148298

2: Crystal structure of the ubiquitin-like domain of human TBK1. Li J, Li J, Miyahira A, Sun J, Liu Y, Cheng G, Liang H; Protein Cell. 2012;3:383-391. PMID:22610919