Vanhooke Janeen L, Benning Matthew M, Bauer Cary B, Pike J Wesley, DeLuca Hector F
Department of Biochemistry, University of Wisconsin-Madison, 53711, USA.
Biochemistry. 2004 Apr 13;43(14):4101-10. doi: 10.1021/bi036056y.
We have determined the crystal structures of the ligand binding domain (LBD) of the rat vitamin D receptor in ternary complexes with a synthetic LXXLL-containing peptide and the following four ligands: 1alpha,25-dihydroxyvitamin D(3); 2-methylene-19-nor-(20S)-1alpha,25-dihydroxyvitamin D(3) (2MD); 1alpha-hydroxy-2-methylene-19-nor-(20S)-bishomopregnacalciferol (2MbisP), and 2alpha-methyl-19-nor-1alpha,25-dihydroxyvitamin D(3) (2AM20R). The conformation of the LBD is identical in each complex. Binding of the 2-carbon-modified analogues does not change the positions of the amino acids in the ligand binding site and has no effect on the interactions in the coactivator binding pocket. The CD ring of the superpotent analogue, 2MD, is tilted within the binding site relative to the other ligands in this study and to (20S)-1alpha,25-dihydroxyvitamin D(3) [Tocchini-Valentini et al. (2001) Proc. Natl. Acad. Sci. U.S.A. 98, 5491-5496]. The aliphatic side chain of 2MD follows a different path within the binding site; nevertheless, the 25-hydroxyl group at the end of the chain occupies the same position as that of the natural ligand, and the hydrogen bonds with histidines 301 and 393 are maintained. 2MbisP binds to the receptor despite the absence of the 25-hydroxyl group. A water molecule is observed between His 301 and His 393 in this structure, and it preserves the orientation of the histidines in the binding site. Although the alpha-chair conformer is highly favored in solution for the A ring of 2AM20R, the crystal structures demonstrate that this ring assumes the beta-chair conformation in all cases, and the 1alpha-hydroxyl group is equatorial. The peptide folds as a helix and is anchored through hydrogen bonds to a surface groove formed by helices 3, 4, and 12. Electrostatic and hydrophobic interactions between the peptide and the LBD stabilize the active receptor conformation. This stablization appears necessary for crystal growth.
我们已确定大鼠维生素D受体的配体结合结构域（LBD）与含LXXLL的合成肽及以下四种配体形成的三元复合物的晶体结构：1α,25 - 二羟基维生素D₃；2 - 亚甲基 - 19 - 去甲 -（20S）- 1α,25 - 二羟基维生素D₃（2MD）；1α - 羟基 - 2 - 亚甲基 - 19 - 去甲 -（20S）- 双高孕甾钙化醇（2MbisP），以及2α - 甲基 - 19 - 去甲 - 1α,25 - 二羟基维生素D₃（2AM20R）。在每个复合物中，LBD的构象是相同的。2 - 碳修饰类似物的结合不会改变配体结合位点中氨基酸的位置，并且对共激活因子结合口袋中的相互作用没有影响。在本研究中，超强效类似物2MD的CD环相对于其他配体以及（20S）- 1α,25 - 二羟基维生素D₃ [Tocchini - Valentini等人（2001年）。美国国家科学院院刊98, 5491 - 5496] 在结合位点内发生倾斜。2MD的脂肪族侧链在结合位点内遵循不同的路径；然而，链末端的25 - 羟基占据与天然配体相同的位置，并且与组氨酸301和393的氢键得以维持。尽管没有25 - 羟基，2MbisP仍与受体结合。在该结构中，观察到组氨酸301和组氨酸393之间有一个水分子，并且它保持了结合位点中组氨酸的取向。尽管对于2AM20R的A环，α - 椅式构象在溶液中高度有利，但晶体结构表明在所有情况下该环都呈现β - 椅式构象，并且1α - 羟基是平伏的。该肽折叠成螺旋状，并通过氢键锚定到由螺旋3、4和12形成的表面凹槽。肽与LBD之间的静电和疏水相互作用稳定了活性受体构象。这种稳定作用对于晶体生长似乎是必要的。
