PMID: 27851956

Authors:

Polley S, Passos DO, Huang DB, Mulero MC, Mazumder A, Biswas T, Verma IM, Lyumkis D, Ghosh G

Title:

Structural Basis for the Activation of IKK1/alpha.

Journal:

Cell Rep. 2016 Nov 15;17(8):1907-1914. doi: 10.1016/j.celrep.2016.10.067.

Abstract:

Distinct signaling pathways activate the NF-kappaB family of transcription factors. The canonical NF-kappaB-signaling pathway is mediated by IkappaB kinase 2/beta (IKK2/beta), while the non-canonical pathway depends on IKK1/alpha. The structural and biochemical bases for distinct signaling by these otherwise highly similar IKKs are unclear. We report single-particle cryoelectron microscopy (cryo-EM) and X-ray crystal structures of human IKK1 in dimeric ( approximately 150 kDa) and hexameric ( approximately 450 kDa) forms. The hexamer, which is the representative form in the crystal but comprises only approximately 2% of the particles in solution by cryo-EM, is a trimer of IKK1 dimers. While IKK1 hexamers are not detectable in cells, the surface that supports hexamer formation is critical for IKK1-dependent cellular processing of p100 to p52, the hallmark of non-canonical NF-kappaB signaling. Comparison of this surface to that in IKK2 indicates significant divergence, and it suggests a fundamental role for this surface in signaling by these kinases through distinct pathways.