Structural Insights into the Functions of TBK1 in Innate Antimicrobial Immunity

Tank-binding kinase 1 (TBK1) is a serine/threonine protein-kinase mediating innate antimicrobial immunity. TBK1 is involved in the signaling of TLRs, RLRs, and STING-mediated sensing of cytosolic DNA. Stimulation of these receptors results in the activation of TBK1, which phosphorylates interferon regulatory factor (IRF)-3. Phosphorylated IRF-3 translocates into the nucleus to initiate the transcription of the interferon (IFN)-β gene. Here, we show that TBK1 is activated by autophosphorylation at residue Ser172. Structures of TBK1 bound to two inhibitors showed that TBK1 has the IκB kinase fold with three distinct domains: the kinase domain, the ubiquitin-like domain, and the scaffold and dimerization domain. However, the overall structures of the TBK1 monomer and its dimer are different from IKKβ in the arrangements of the three domains and in dimer formation. Phosphorylation of IRF-3 by TBK1 in vitro results in its oligomerization, and phosphorylation of residue Ser386 plays a key role in IRF-3 activation. •TBK1 is activated by autophosphorylation at residue Ser172•TBK1 exhibits three structural domains similar to IκB kinase•The kinase domain of TBK1 exhibits rigid structure•Phosphorylation of IRF-3 by TBK1 results in the oligomerization of IRF-3 TBK1 is a protein kinase that mediates innate antimicrobial immunity and, upon infection, phosphorylates interferon regulatory factor IRF-3 and initiates antimicrobial defense. Shu et al. determined a structure of mouse TBK1 that provides insights into the roles of TBK1 in antimicrobial immunity.