The RelA nuclear localization signal folds upon binding to I?B?.

ABSTRACT: The nuclear localization signal (NLS) polypeptide of RelA, the canonical nuclear factor-?B family member, is responsible for regulating the nuclear localization of RelA-containing nuclear factor-?B 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 I?B?, 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 I?B? under solution conditions, we conducted NMR and isothermal titration calorimetry studies using a truncated form of I?B? 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 I?B?, the resonance dispersion in the NMR spectrum is significantly greater, providing definitive evidence that the RelA NLS polypeptide folds upon binding I?B?. 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 I?B?-bound RelA NLS polypeptide, is critical for the binding of the RelA NLS polypeptide to I?B?. These results help to explain the role of helix 4 in mediating the high affinity of RelA for I?B?.

SUBMITTER: Cervantes CF 

PROVIDER: S-EPMC3056351 | biostudies-literature | 2011 Jan

REPOSITORIES: biostudies-literature