The human IKKβ subunit kinase domain displays CK2-like phosphorylation specificity

NF-kappa B activation in response to pro-inflammatory stimuli relies upon phosphorylation of I kappa B alpha at serines 32 and 36 by the P subunit of the IK beta kinase complex (IKK). In this study, we build upon the observation that highly purified human IKK beta subunit preparations retain this specificity in vitro. We show that IKK beta constructs that lack their carboxy-terminus beginning at the leucine zipper motif fail to phosphorylate IKB alpha at Ser-32 and Ser-36. Rather, these constructs, which contain the entire IKK beta subunit kinase domain, phosphorylate serine and threonine residues contained within the I kappa B alpha carboxy-terminal PEST region. Furthermore, removal of the leucine zipper and helix-loop-helix regions converts IKK beta to monomer. We propose that the helix-loop-helix of the human IKK beta subunit is necessary for restricting substrate specificity toward Ser-32 and Ser-36 in I kappa B alpha and that in the absence of its carboxy-terminal protein. structural motifs the human IKK beta Subunit kinase domain exhibits a CK2-like phosphorylation specificity. (C) 2008 Elsevier Inc. All rights reserved.