Latimer M, Ernst M K, Dunn L L, Drutskaya M, Rice N R
Molecular Basis of Carcinogenesis Laboratory, ABL-Basic Research Program, National Cancer Institute-Frederick Cancer Research and Development Center, Maryland 21701, USA.
Mol Cell Biol. 1998 May;18(5):2640-9. doi: 10.1128/MCB.18.5.2640.
Members of the Rel/NF-kappaB family of transcription factors are related to each other over a region of about 300 amino acids called the Rel Homology Domain (RHD), which governs DNA binding, dimerization, and binding to inhibitor. At the C-terminal end of the RHD, each protein has a nuclear localization signal (NLS). The crystal structures of the p50 and RelA family members show that the RHD consists of two regions: an N-terminal section which contains some of the DNA contacts and a C-terminal section which contains the remaining DNA contacts and controls dimerization. In unstimulated cells, the homo- or heterodimeric Rel/NF-kappaB proteins are cytoplasmic by virtue of binding to an inhibitor protein (IkappaB) which somehow masks the NLS of each member of the dimer. The IkappaB proteins consist of an ankyrin-repeat-containing domain that is required for binding to dimers and N- and C-terminal domains that are dispensable for binding to most dimers. In this study, we examined the interaction between IkappaB alpha and Rel family homodimers by mutational analysis. We show that (i) the dimerization regions of p50, RelA, and c-Rel are sufficient for binding to IkappaB alpha, (ii) the NLSs of RelA and c-Rel are not required for binding to IkappaB alpha but do stabilize the interaction, (iii) the NLS of p50 is required for binding to IkappaB alpha, (iv) only certain residues within the p50 NLS are required for binding, and (v) in a p50-IkappaB alpha complex or a c-Rel-IkappaB alpha complex, the N terminus of IkappaB alpha either directly or indirectly masks one or both of the dimer NLSs.
转录因子Rel/NF-κB家族的成员在一个约300个氨基酸的区域内彼此相关，该区域称为Rel同源结构域（RHD），它控制DNA结合、二聚化以及与抑制剂的结合。在RHD的C末端，每个蛋白质都有一个核定位信号（NLS）。p50和RelA家族成员的晶体结构表明，RHD由两个区域组成：一个N末端部分，包含一些与DNA的接触位点；一个C末端部分，包含其余的DNA接触位点并控制二聚化。在未受刺激的细胞中，同源或异源二聚体Rel/NF-κB蛋白定位于细胞质，这是因为它们与一种抑制剂蛋白（IkappaB）结合，该抑制剂以某种方式掩盖了二聚体每个成员的NLS。IkappaB蛋白由一个与二聚体结合所需的含锚蛋白重复序列的结构域以及对大多数二聚体结合而言并非必需的N末端和C末端结构域组成。在本研究中，我们通过突变分析研究了IkappaBα与Rel家族同源二聚体之间的相互作用。我们发现：（i）p50、RelA和c-Rel的二聚化区域足以与IkappaBα结合；（ii）RelA和c-Rel的NLS对与IkappaBα的结合不是必需的，但能稳定这种相互作用；（iii）p50的NLS是与IkappaBα结合所必需的；（iv）与IkappaBα结合仅需要p50 NLS内的某些残基；（v）在p50-IkappaBα复合物或c-Rel-IkappaBα复合物中，IkappaBα的N末端直接或间接掩盖二聚体的一个或两个NLS。
