Visualization of the nanospring dynamics of the IκBα ankyrin repeat domain in real time

Jorge A. Lamboy, Hajin Kimb, Kyung Suk Lee, Taekjip Ha, and Elizabeth A. Komives


IκBα is a crucial regulator of NFκB transcription. NFκB-mediated gene activation is robust because levels of free IκBα are kept extremely low by rapid, ubiquitin-independent degradation of newly synthesized IκBα. IκBα has a weakly folded ankyrin repeat 5–6 (AR5–6) region that is critical in establishing its short intracellular half-life. The AR5–6 region of IκBα folds upon binding to NFκB. The NFκB-bound IκBα has a long half-life and requires ubiquitin-targeted degradation. We present single molecule FRET evidence that the native state of IκBα transiently populates an intrinsically disordered state characterized by a more extended structure and fluctuations on the millisecond time scale. Binding to NFκB or introduction of stabilizing mutations in AR 6 suppressed the fluctuations, whereas higher temperature or small amounts of urea increased them. The results reveal that intrinsically disordered protein regions transition between collapsed and extended conformations under native conditions.


DOI


Journal: Proceedings of the National Academy of Sciences