Hormone Research Center, School of Biological Sciences and Technology, Chonnam National University, Gwangju 500-757, Republic of Korea.
J Mol Biol. 2010 Feb 26;396(3):747-60. doi: 10.1016/j.jmb.2009.12.008. Epub 2009 Dec 16.
The unliganded nuclear receptor (NR) generally recruits the NR corepressor (N-CoR) and the silencing mediator of retinoid and thyroid hormone receptor via its direct binding to the extended helical motif within dual NR-interaction domains (IDs) of corepressors. Interestingly, N-CoR has a third ID (ID3) upstream of two IDs (ID1 and ID2) and its core motif (IDVII), rather than an extended helical motif, is known to be involved directly in the exclusive interaction of ID3 with the thyroid hormone receptor (TR). Here, we investigated the molecular determinants of the TR interaction with ID3 to understand the molecular basis of the N-CoR preference shown by the TR homodimer. Using a one- plus two-hybrid system, we identified the specific residues of N-CoR-ID2 and N-CoR-ID3 that are required for stable association of N-CoR with the TR homodimer. By swapping experiments and mutagenesis studies, we found that the C-terminally flanked residues of the core motif of ID3 contribute to the TR preference for N-CoR-ID3, suggesting that an extended three-turn helix might form within the ID3 via a C-terminal extension (IDVIITRQI) and participate directly in the TR-specific interaction. Structural modeling of the ID3 motif on TR-LBD is consistent with this conclusion. Notably, we identified a novel interaction between N-CoR-ID3 and orphan NR RevErb that is mediated by the residues crucial also in TR binding. These observations raise the intriguing possibility that NR homodimers such as TR and RevErb display preferential binding to the N-CoR corepressor via their specific interactions with ID3, which is normally absent from the silencing mediator of retinoid and thyroid hormone receptor.
无配体的核受体（NR）通常通过其直接结合到核心抑制因子的双 NR 相互作用结构域（IDs）内的扩展螺旋基序，募集 NR 核心抑制因子（N-CoR）和沉默调节剂的视黄酸和甲状腺激素受体。有趣的是，N-CoR 在两个 ID（ID1 和 ID2）的上游有第三个 ID（ID3），其核心基序（IDVII）而不是扩展的螺旋基序，已知直接参与 ID3 与甲状腺激素受体（TR）的特异性相互作用。在这里，我们研究了 TR 与 ID3 的相互作用的分子决定因素，以了解 TR 二聚体显示的 N-CoR 偏好的分子基础。使用一加上双杂交系统，我们确定了 N-CoR-ID2 和 N-CoR-ID3 的特定残基，这些残基对于 N-CoR 与 TR 二聚体的稳定结合是必需的。通过交换实验和突变研究，我们发现 ID3 核心基序的 C 末端侧翼残基有助于 TR 对 N-CoR-ID3 的偏好，这表明通过 C 末端延伸（IDVIITRQI）可能在 ID3 内形成一个三转角螺旋，并直接参与 TR 特异性相互作用。ID3 基序在 TR-LBD 上的结构建模与这一结论一致。值得注意的是，我们发现 N-CoR-ID3 与孤儿 NR RevErb 之间存在新的相互作用，这种相互作用是由在 TR 结合中也至关重要的残基介导的。这些观察结果提出了一个有趣的可能性，即 NR 二聚体，如 TR 和 RevErb，通过与 ID3 的特异性相互作用，显示出对 N-CoR 核心抑制因子的优先结合，而这种相互作用通常不存在于视黄酸和甲状腺激素受体的沉默调节剂中。
