Browning Christopher, Martin Elyette, Loch Caroline, Wurtz Jean-Marie, Moras Dino, Stote Roland H, Dejaegere Annick P, Billas Isabelle M L
Département de Biologie et de Génomique Structurales, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Ecole Supérieure de Biotechnologie de Strasbourg, Boulevard Sébastien Brant, Illkirch, France.
J Biol Chem. 2007 Nov 9;282(45):32924-34. doi: 10.1074/jbc.M705559200. Epub 2007 Sep 11.
The insect steroid hormone 20-hydroxyecdysone (20E) binds to its cognate nuclear receptor composed of the ecdysone receptor (EcR) and Ultraspiracle (USP) and triggers the main developmental transitions, in particular molting and metamorphosis. We present the crystal structure of the ligand-binding domains of EcR/USP in complex with 20E at 2.4A resolution and compare it with published structures of EcR/USP bound to ponasterone A (ponA). ponA is essentially identical to 20E but lacks the 25-OH group of 20E. The structure of 20E-bound EcR indicates that an additional hydrogen bond is formed compared with the ponA-bound receptor, yet, paradoxically, ponA has a significantly higher affinity for EcR than 20E. Theoretical studies based on docking and free energy methods lead to a rationale for understanding the difference in binding affinities between 20E and ponA. Results of the calculations indicate that the favorable contribution from the extra H-bond made by 25-OH of 20E is counterbalanced by its larger desolvation cost compared with that of ponA. The contribution of 25-OH to the binding affinity is further compared with those of 20- and 22-OH groups. Ligands that lack the 20- or 22-OH group are indeed known to bind less favorably to EcR than 20E, an effect opposite to that observed for ponA. The results indicate that their respective contributions to receptor-ligand complex stability reside mostly in their different contributions to solvation/desolvation. Together, the data demonstrate the critical role of ligand desolvation in determining binding affinity, with general implications for the binding of hormones to their cognate nuclear receptors.
昆虫类固醇激素20-羟基蜕皮酮（20E）与其由蜕皮激素受体（EcR）和超气门蛋白（USP）组成的同源核受体结合，并触发主要的发育转变，特别是蜕皮和变态。我们以2.4埃的分辨率展示了EcR/USP配体结合结构域与20E复合物的晶体结构，并将其与已发表的EcR/USP与紫衫甾酮A（ponA）结合的结构进行比较。ponA与20E基本相同，但缺少20E的25-羟基基团。与结合ponA的受体相比，结合20E的EcR结构表明形成了一个额外的氢键，但矛盾的是，ponA对EcR的亲和力明显高于20E。基于对接和自由能方法的理论研究为理解20E和ponA之间结合亲和力的差异提供了理论依据。计算结果表明，20E的25-羟基形成的额外氢键的有利贡献被其与ponA相比更大的去溶剂化成本所抵消。进一步比较了25-羟基与20-和22-羟基对结合亲和力的贡献。已知缺少20-或22-羟基基团的配体与EcR的结合不如20E有利，这一效应与ponA观察到的相反。结果表明，它们对受体-配体复合物稳定性的各自贡献主要在于它们对溶剂化/去溶剂化的不同贡献。总之，这些数据证明了配体去溶剂化在决定结合亲和力中的关键作用，对激素与其同源核受体的结合具有普遍意义。
