title: The RelA nuclear localization signal folds upon binding to IκBα.
abstract: The nuclear localization signal (NLS) polypeptide of RelA, the canonical nuclear factor-κB family member, is responsible for regulating the nuclear localization of RelA-containing nuclear factor-κB dimers. The RelA NLS polypeptide also plays a crucial role in mediating the high affinity and specificity of the interaction of RelA-containing dimers with the inhibitor IκBα, forming two helical motifs according to the published X-ray crystal structure. In order to define the nature of the interaction between the RelA NLS and IκBα under solution conditions, we conducted NMR and isothermal titration calorimetry studies using a truncated form of IκBα containing residues 67-206 and a peptide spanning residues 293-321 of RelA. The NLS peptide, although largely unfolded, has a weak tendency toward helical structure when free in solution. Upon addition of the labeled peptide to unlabeled IκBα, the resonance dispersion in the NMR spectrum is significantly greater, providing definitive evidence that the RelA NLS polypeptide folds upon binding IκBα. Isothermal titration calorimetry studies of single-point mutants reveal that residue F309, which is located in the middle of the more C-terminal of the two helices (helix 4) in the IκBα-bound RelA NLS polypeptide, is critical for the binding of the RelA NLS polypeptide to IκBα. These results help to explain the role of helix 4 in mediating the high affinity of RelA for IκBα.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92092-0378, USA.
authors.forename: Carla F
authors.initials: CF
authors.lastname: Cervantes
authors.forename: Simon
authors.initials: S
authors.lastname: Bergqvist
authors.forename: Magnus
authors.initials: M
authors.lastname: Kjaergaard
authors.forename: Gerard
authors.initials: G
authors.lastname: Kroon
authors.forename: Shih-Che
authors.initials: SC
authors.lastname: Sue
authors.forename: H Jane
authors.initials: HJ
authors.lastname: Dyson
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Komives
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D006801:Humans; D020672:I-kappa B Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D000072000:NF-KappaB Inhibitor alpha; D019913:Nuclear Localization Signals / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D051996:Transcription Factor RelA / Q000737:chemistry* / Q000378:metabolism
chemical_list: D020672:I-kappa B Proteins; C000606204:NFKBIA protein, human; D019913:Nuclear Localization Signals; D051996:Transcription Factor RelA; D000072000:NF-KappaB Inhibitor alpha