Crystal Structure of a Human IκB Kinase β Asymmetric Dimer

Abstract

Background: IB kinase ␤ is a key regulator in the NB signaling pathway. Results: Crystal structure of a human IKK␤ asymmetric dimer shows one kinase active site phosphorylated and in the active conformation and the other unphosphorylated and inactive. Conclusion: Depending on the phosphorylation state, IKK␤ can adopt distinct dimeric geometry. Significance: High resolution structure of hIKK␤ provides structural basis for its activation and potential use of inhibitor design.

Novel Lys63-linked ubiquitination of IKKβ induces STAT3 signaling

“…30 A comparison of other species shows this region to be highly conserved among IKKb orthologs (Table 2A). Even more surprising is the very strict conservation of this region, including the Lys corresponding to Lys147 of IKKb, in a very large number of human kinase paralogs (Table 2B).…”

“…We demonstrate that the mutation K171E leads to constitutive activation of the intrinsic kinase activity of IKKb, suggesting a role of the normal Lys171 side chain in stabilizing an inactive kinase in addition to its www.landesbioscience.comdocumented importance in the activated structure. 30 Other mutations at this position also result in constitutive activation of IKKb, demonstrated by in vitro kinase assay and phosphorylation of the activation loop residues S177/S181. Such mutations also result in significant activation of STAT3 signaling, which is independent of TNFa or IL-6 stimulation.…”

“…29 In addition, Lys171 contributes to the stability of the activated protein via ionic interactions with phosphorylated Ser181. 30 Hence, this residue plays a critical regulatory role in the activated structure. IKKb mutant proteins were expressed in HEK293 cells and the IKK complex was immunoprecipitated with IKKg antisera and assayed for in vitro phosphorylation.…”

IκB Kinase β (IKBKB) Mutations in Lymphomas That Constitutively Activate Canonical Nuclear Factor κB (NFκB) Signaling

“…Lysine 171 of IKK␤ is a residue that is located parallel to the phosphorylation site in the activation loop. Examination of the structure of phosphorylated versus non-phosphorylated (27) IKK␤ revealed that this residue is part of a cationic pocket, also made up of Arg-57 in the C-terminal helix and Arg-144 in the catalytic loop. The recently resolved structure of human IKK␤ suggests that in its active conformation, the activation loop phosphoserine 181 interacts with these cationic pocket residues, including lysine 171, to switch the kinase domain to a catalytically active conformation.…”

“…2, A and B) and active (Figs. 2, C and D) structures of this kinase based on the recently published structure of human IKK␤ (27) shows striking differences between the two states. In the active, phosphorylated IKK␤, the negatively charged phosphate moi- ety on serine 181 makes electrostatic interactions with cationic pocket residues Arg-57, Arg-144, and Lys-171, located, respectively, in the C-terminal helix, catalytic loop, and activation loop (Fig.…”