Studies of estrogen receptor structure using molecular dynamics

在未成熟雄性虹鳟（rt）肝细胞原代培养中，卵黄原蛋白（Vg）基因的表达受E2通过雌激素受体（ER）调控。然而，雌激素以外的类固醇也能刺激Vg基因的表达。这些类固醇在孵育期间很难转化为E2，它们的刺激活性被他莫昔芬完全抑制，这意味着它与rtER有关。这些类固醇在康诺利表面不带正电荷或带少量正电荷。相比之下，未能刺激Vg基因表达的类固醇由于极化，在C环和D环周围有很强的正电荷或负电荷。rtER与人ERa的配体结合域（LBD）氨基酸序列同源性为57.7%；假定的类固醇结合位点只有一个氨基酸不同。我们利用hERa的x射线晶体学数据模拟了rtER的LBD的三维结构，以研究类固醇与rtER之间的配合（结构和静电）。与rtER结合有两个重要因素：(i)甾体的C3和C17（亲水区）附近的羟基或羰基si可以与His（489）、Arg（359）和Glu（318）形成氢键；（ii）疏水甾体核通过范德华力与rtER LBD的疏水区相互作用。如果极性官能团存在，类固醇和rtER LBD之间的疏水相互作用被大大削弱。

In primary cultures of immature male rainbow trout (rt) hepatocytes, vitellogenin (Vg) gene expression regulated by E2 via the estrogen receptor (ER). However, steroids other than estrogens can also stimulate Vg gene expression. These steroids are hardly converted into E2 during incubation and their stimulatory activity is completely inhibited by tamoxifen implying rtER involvement. These steroids have no or a slightly positive charge on the Connolly surface. In contrast, steroids that failed to stimulate Vg gene expression had a strong positive or negative charge around rings C and D due to polarization. The ammo acid sequences of the ligand binding domains (LBD) of rtER and human ERa have 57.7% homology; only one amino acid differs in the presumed steroid binding site. We modeled the three-dimensional structure of the LBD of rtER using X-ray crystallographic data for hERa in order to investigate the fit (structural and electrostatic) between steroid and rtER. Two factors are essential for binding to rtER: (i) hydroxyl or carbonyl groupsi near C3 andI C17 of the steroids (hydrophilic regions) that can form hydrogen bonds with His(489), Arg(359) and Glu(318), (ii) a hydrophobic steroid nucleus that interacts with a hydrophobic region of the rtER LBD through van der Waals forces. If polar functional groups are present, the hydrophobic interaction between steroid and the rtER LBD is considerably weakened.