Holmbeck S M, Foster M P, Casimiro D R, Sem D S, Dyson H J, Wright P E
Department of Molecular Biology and Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla,, CA 92037, USA.
J Mol Biol. 1998 Aug 14;281(2):271-84. doi: 10.1006/jmbi.1998.1908.
The retinoid X receptor (RXR) is a member of the nuclear hormone receptor superfamily of transcriptional regulators and plays a central role in the retinoid and, through its ability to heterodimerize with other nuclear hormone receptors, non-steroid signaling pathways. The DNA-binding and recognition functions of RXR are located in a conserved 83 amino acid residue domain that recognizes the consensus sequence AGGTCA. In order to provide a detailed picture of its structure, we have calculated a high-resolution solution structure of the C195A RXRalpha DNA-binding domain. Structures were calculated using 1131 distance and dihedral angle constraints derived from 1H, 13C and 15N NMR spectra. The structures reveal a perpendicularly packed, "loop-helix" fold similar to other nuclear hormone receptor DNA-binding domains and confirm the existence of the C-terminal helix, which was first observed in the low-resolution NMR structure. The C-terminal helix is well formed and is stabilized by packing interactions with residues in the hydrophobic core. The solution structure of RXR is very similar to that determined by X-ray crystallographic studies of the RXR-TR heterodimer complex with DNA, except that in the latter case no electron density was observed for residues corresponding to the C-terminal helix. Other differences between the X-ray and NMR structures occur in the second zinc-binding loop, which is disordered in solution. Heteronuclear 15N NOE measurements suggest that this loop has enhanced flexibility in the free protein.
维甲酸X受体（RXR）是转录调节因子核激素受体超家族的成员，在维甲酸信号通路中起核心作用，并且通过与其他核激素受体形成异源二聚体的能力，在非甾体信号通路中也发挥作用。RXR的DNA结合和识别功能位于一个由83个氨基酸残基组成的保守结构域中，该结构域可识别共有序列AGGTCA。为了详细了解其结构，我们计算了C195A RXRα DNA结合结构域的高分辨率溶液结构。结构计算使用了来自1H、13C和15N NMR光谱的1131个距离和二面角约束。这些结构揭示了一种垂直堆积的“环-螺旋”折叠，类似于其他核激素受体DNA结合结构域，并证实了C端螺旋的存在，这在低分辨率NMR结构中首次观察到。C端螺旋结构良好，并通过与疏水核心中的残基进行堆积相互作用而稳定。RXR的溶液结构与通过对RXR-TR异源二聚体与DNA复合物的X射线晶体学研究确定的结构非常相似，只是在后一种情况下，未观察到与C端螺旋相对应的残基的电子密度。X射线结构和NMR结构之间的其他差异出现在第二个锌结合环中，该环在溶液中是无序的。异核15N NOE测量表明，该环在游离蛋白中具有更高的灵活性。
