Crystal Structure of a Human IaB Kinase ß Asymmetric Dimer

SUMMARY

Phosphorylation of inhibitor of nuclear  transcription factor B (IB) by IB  kinase (IKK) triggers the degradation of  IB and migration of cytoplasmic B to  the nucleus where it promotes the  transcription of its target genes.  Activation of IKK is achieved by phosphorylation of its main subunit,  IKK at the activation loop sites. Here  we report the 2.8 Å resolution crystal  structure of human IKKhIKK which  is partially phosphorylated and bound to the staurosporine analog K252a. The  hIKK protomer adopts a trimodular  structure that closely resembles that from  Xenopus laevis (xIKK: an N-terminal  kinase domain (KD), a central ubiquitinlike domain (ULD), and a C-terminal  dimerization domain (SDD). Although  hIKK and xIKK utilize a similar  dimerization mode, their overall  geometries are distinct. In contrast to the  structure resembling closed shears  reported previously for xIKK hIKK exists as an open asymmetric dimer in  which the two KDs are further apart,  with one in an active and the other in an  inactive conformation. Dimer  interactions are limited to the C-terminal  six-helix bundle that acts as a hinge  between the two subunits. The observed  domain movements in the structures of  IKK may represent transphosphorylation steps that accompany  IKK activation.

This article was published online in The Journal of Biological Chemistry and is free to access.