X-ray crystal structure of proto-oncogene product c-Rel bound to the CD28 response element of IL-2

Structure. 2001 Aug;9(8):669-78. doi: 10.1016/s0969-2126(01)00635-9.


Background: The proto-oncogene product c-Rel is a Rel/NF-kappaB family transcription factor that plays a critical role in lymphoid cell development and mediates CD28-induced expression of interleukin 2 (IL-2). The CD28 response element (CD28RE) in the IL-2 enhancer is nonameric and similar to the kappaB DNA target sites recognized by p65 homodimers.

Results: We have determined and refined the X-ray crystal structure of the c-Rel homodimer complexed to the CD28RE DNA site, 5'-AGAAATTCC-3', to 2.85 A resolution. The c-Rel homodimer binds CD28RE in a mode similar to that observed in the p65/IL-8 kappaB crystallographic complex. Binding studies reveal that the c-Rel homodimer recognizes the CD28RE with higher affinity as compared to other canonical kappaB sequences despite the nonconsensus A:T base pair at the 5' end of the CD28RE. Preferential recognition of the CD28RE by c-Rel results from the direct contacts between the protein and the DNA as well as intrasubunit interactions between the beta(f)-beta(g) loop in the dimerization domain and the DNA-contacting loop L1 of the N-terminal domain. Not only do these loops have different conformations in other Rel/DNA crystallographic complexes, but they also contain two of the five oncogenic point mutations found in v-Rel.

Conclusions: The current structure indicates that a non-DNA-contacting loop in the dimerization domain and the DNA-contacting loop L1 may play critical roles in defining affinity and specificity. Two amino acid changes in these segments may account for the differential DNA binding by v-Rel as compared to that of c-Rel.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Anisotropy
  • Base Sequence
  • CD28 Antigens / chemistry*
  • Chickens
  • Crystallography, X-Ray
  • DNA / metabolism
  • Dimerization
  • Dose-Response Relationship, Drug
  • Escherichia coli / metabolism
  • Interleukin-2 / chemistry*
  • Models, Molecular
  • Molecular Sequence Data
  • Mutation
  • NF-kappa B / chemistry
  • Oncogene Proteins v-rel / metabolism
  • Point Mutation
  • Protein Binding
  • Protein Structure, Tertiary
  • Proto-Oncogene Proteins c-rel / chemistry*
  • Sequence Homology, Amino Acid
  • Spectrometry, Fluorescence


  • CD28 Antigens
  • Interleukin-2
  • NF-kappa B
  • Oncogene Proteins v-rel
  • Proto-Oncogene Proteins c-rel
  • DNA

Associated data

  • PDB/1GJI