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Structure of an IkappaBalpha/NF-kappaB complex

M D Jacobs1, S C Harrison

  • 1Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.

Cell
|December 29, 1998
PubMed

Insights

The inhibitory protein IkappaBalpha binds transcription factor NF-kappaB, preventing its nuclear entry. X-ray crystallography reveals the structural basis for this interaction, crucial for regulating immune responses.

Area of Science:

  • Molecular Biology
  • Structural Biology
  • Immunology

Background:

  • Nuclear factor-kappaB (NF-kappaB) is a key transcription factor regulating immune responses and inflammation.
  • IkappaBalpha acts as a cytoplasmic inhibitor, sequestering NF-kappaB and preventing its translocation to the nucleus.
  • Understanding the structural basis of IkappaBalpha-NF-kappaB interaction is critical for deciphering NF-kappaB pathway regulation.

Purpose of the Study:

  • To determine the high-resolution crystal structure of the IkappaBalpha ankyrin repeat domain complexed with a truncated NF-kappaB heterodimer (p50/p65).
  • To elucidate the molecular interactions governing the inhibition of NF-kappaB by IkappaBalpha.

Main Methods:

  • X-ray crystallography was employed to determine the structure at 2.7 Angstrom resolution.
  • Analysis of the protein complex structure to identify specific contact points and orientations.

Main Results:

  • The structure reveals six IkappaBalpha ankyrin repeats interacting with the C-terminal domains of NF-kappaB Rel homology regions.
  • Discontinuous contact patches suggest a combinatorial mechanism for ankyrin repeat specificity.
  • The N-terminal region of IkappaBalpha, including the p65 nuclear localization signal, is positioned within the complex.
  • The sixth ankyrin repeat indicates that full-length IkappaBalpha would block the NF-kappaB DNA-binding cleft.

Conclusions:

  • The determined structure provides a detailed molecular mechanism for NF-kappaB inhibition by IkappaBalpha.
  • The findings highlight the role of ankyrin repeat interactions in regulating transcription factor activity.
  • The structural insights are valuable for understanding NF-kappaB pathway regulation in cellular processes and disease.

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