Department of Biochemistry, Yokohama City University Graduate School of Medicine, Yokohama 236-0004, Japan.
College of Life Sciences, Ritsumeikan University, Kusatsu 525-8577, Japan.
Nucleic Acids Res. 2022 Nov 28;50(21):12543-12557. doi: 10.1093/nar/gkac1102.
Several basic leucine zipper (bZIP) transcription factors have accessory motifs in their DNA-binding domains, such as the CNC motif of CNC family or the EHR motif of small Maf (sMaf) proteins. CNC family proteins heterodimerize with sMaf proteins to recognize CNC-sMaf binding DNA elements (CsMBEs) in competition with sMaf homodimers, but the functional role of the CNC motif remains elusive. In this study, we report the crystal structures of Nrf2/NFE2L2, a CNC family protein regulating anti-stress transcriptional responses, in a complex with MafG and CsMBE. The CNC motif restricts the conformations of crucial Arg residues in the basic region, which form extensive contact with the DNA backbone phosphates. Accordingly, the Nrf2-MafG heterodimer has approximately a 200-fold stronger affinity for CsMBE than canonical bZIP proteins, such as AP-1 proteins. The high DNA affinity of the CNC-sMaf heterodimer may allow it to compete with the sMaf homodimer on target genes without being perturbed by other low-affinity bZIP proteins with similar sequence specificity.
几种基本亮氨酸拉链(bZIP)转录因子在其 DNA 结合域中具有辅助基序，例如 CNC 家族的 CNC 基序或小 Maf(sMaf)蛋白的 EHR 基序。CNC 家族蛋白与 sMaf 蛋白异二聚化以识别与 sMaf 同源二聚体竞争的 CNC-sMaf 结合 DNA 元件(CsMBEs)，但 CNC 基序的功能作用仍不清楚。在这项研究中，我们报告了调节抗应激转录反应的 CNC 家族蛋白 Nrf2/NFE2L2 与 MafG 和 CsMBE 形成复合物的晶体结构。CNC 基序限制了碱性区域中关键 Arg 残基的构象，这些 Arg 残基与 DNA 骨架磷酸形成广泛的接触。因此，Nrf2-MafG 异二聚体与典型的 bZIP 蛋白(如 AP-1 蛋白)相比，对 CsMBE 的亲和力约高 200 倍。CNC-sMaf 异二聚体的高 DNA 亲和力可能使其能够在不被其他具有相似序列特异性的低亲和力 bZIP 蛋白干扰的情况下，与 sMaf 同源二聚体竞争靶基因。
