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Direct phosphorylation of IkappaB by IKKalpha and IKKbeta: discrimination between free and NF-kappaB-bound substrate.

A large protein complex mediates the phosphorylation of the inhibitor of kappaB (IkappaB), which results in the activation of nuclear factor kappaB (NF-kappaB). Two subunits of this complex, IkappaB kinase alpha (IKKalpha) and IkappaB kinase beta (IKKbeta), are required for NF-kappaB activation. Purified recombinant IKKalpha and IKKbeta expressed in insect cells were used to demonstrate that each protein can directly phosphorylate IkappaB proteins. IKKalpha and IKKbeta were found to form both homodimers and heterodimers. Both IKKalpha and IKKbeta phosphorylated IkappaB bound to NF-kappaB more efficiently than they phosphorylated free IkappaB. This result explains how free IkappaB can accumulate in cells in which IKK is still active and thus can contribute to the termination of NF-kappaB activation.

Pubmed ID: 9721103

Authors

  • Zandi E
  • Chen Y
  • Karin M

Journal

Science (New York, N.Y.)

Publication Data

August 28, 1998

Associated Grants

  • Agency: NIAID NIH HHS, Id: AI 43477

Mesh Terms

  • Animals
  • Cell Line
  • Dimerization
  • Enzyme Activation
  • HeLa Cells
  • Helix-Loop-Helix Motifs
  • Humans
  • I-kappa B Kinase
  • Leucine Zippers
  • Mutation
  • NF-kappa B
  • Phosphorylation
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins
  • Recombinant Fusion Proteins
  • Recombinant Proteins
  • Spodoptera
  • Transcription Factor RelB
  • Transcription Factors