Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA, 19107, USA.
Center of Infectious Disease Research, Walter Reed Army Institute of Research, Silver Spring, MD, USA.
Nat Commun. 2022 Mar 8;13(1):1207. doi: 10.1038/s41467-022-28846-z.
Nuclear translocation of the p50/p65 heterodimer is essential for NF-κB signaling. In unstimulated cells, p50/p65 is retained by the inhibitor IκBα in the cytoplasm that masks the p65-nuclear localization sequence (NLS). Upon activation, p50/p65 is translocated into the nucleus by the adapter importin α3 and the receptor importin β. Here, we describe a bipartite NLS in p50/p65, analogous to nucleoplasmin NLS but exposed in trans. Importin α3 accommodates the p50- and p65-NLSs at the major and minor NLS-binding pockets, respectively. The p50-NLS is the predominant binding determinant, while the p65-NLS induces a conformational change in the Armadillo 7 of importin α3 that stabilizes a helical conformation of the p65-NLS. Neither conformational change was observed for importin α1, which makes fewer bonds with the p50/p65 NLSs, explaining the preference for α3. We propose that importin α3 discriminates between the transcriptionally active p50/p65 heterodimer and p50/p50 and p65/65 homodimers, ensuring fidelity in NF-κB signaling.
核转位的 p50/p65 异二聚体对于 NF-κB 信号转导是必不可少的。在未受刺激的细胞中，p50/p65 被细胞质中的抑制剂 IκBα保留，该抑制剂掩盖了 p65-核定位序列（NLS）。在激活后，p50/p65 通过衔接蛋白 importin α3 和受体 importin β 被转运到细胞核中。在这里，我们描述了 p50/p65 中的二部分 NLS，类似于核质素 NLS，但以反式暴露。Importin α3 在主要和次要 NLS 结合口袋中分别容纳 p50-NLS 和 p65-NLS。p50-NLS 是主要的结合决定因素，而 p65-NLS 诱导 importin α3 的 Armadillo 7 构象变化，稳定 p65-NLS 的螺旋构象。对于 importin α1 没有观察到这种构象变化，它与 p50/p65 NLS 结合较少的键，这解释了对 α3 的偏好。我们提出，importin α3 区分转录活性的 p50/p65 异二聚体和 p50/p50 和 p65/65 同源二聚体，确保 NF-κB 信号转导的保真度。
