已知雌激素受體與乳癌等疾病有關係，雌激素受體藉由與雌激素配位結合而被活化，由文獻上得知其配位結合的鍵結是氫鍵，因此本篇文章使用理論計算方法來對配位結合的氫鍵進行研究，希望對雌激素及其受體的結合機制有所了解。
由RCSB Protein Data Bank下載XRD結構以建立計算座標，本文針對雌激素Estradiol 及三個雌激素類似物Diethylstilbestrol、Raloxifen、4-hydroxytamoxifen，分別探討其與型雌激素受體配位結合的鍵結情形。一開始根據文獻，只探討雌激素及其周圍能與其產生氫鍵的基團Glu353、Arg394、water、Leu387、His524的配位鍵結情形，並使用Gaussian 98軟體以Hartree －Fock方法、密度泛函數方法(DFT)與天然鍵性軌域(NBO)等對整個結構進行最佳化計算，結果發現因Arg394必須移動以使本身產生較多氫鍵，來使整個結構安定，因此得到的結構與原XRD結構不同。由此結構來探討電荷分佈，以及氫鍵的鍵長、鍵角、穩定能、及鍵結軌域電子組態，另發現除了氫鍵外，也有其他donor - acceptor的鍵結。
為了解XRD晶體結構中氫鍵的鍵結情形，使用如上簡化的結構，但固定已知的原子座標，只允許氫移動，然而如此卻無法完成最佳化計算。經多方嘗試後，發現若只限制氮氧等會產生氫鍵原子的相對距離，可得到類似XRD晶體結構的計算結果。
為了探討整個結構是否對氫鍵有影響，目前正嘗試使用ONIOM方法，將整個結構分內外層一同計算，內層為上述簡化結構，外層為其餘全部結構，但外層使用分子力學法，目前已獲得氫鍵鍵長與鍵角的初步結果。

It is known that some diseases such as breast cancer and osteoporosis are related to estrogen receptor (ER). ER is activated by its ligand, estrogens, which are steroid hormone. According to literatures the combination between ER and estrogen is based on hydrogen bonds, so theoretical calculation is applied to study these hydrogen bonds. We hope this study can help us to understand the structure.
Human estrogen, estradiol, and three estrogen-like compounds, Diethylstilbestrol, Raloxifen and 4-hydroxytamoxifen, are studied. They combine with ER- to form 1ERE, 3ERD, 1ERR and 3ERT respectively. The XRD structures which can be downloaded from RCSB Protein Data Bank are used to construct the calculation models. First only estrogen and its surrounding groups, Arg394, Glu353, water, Leu387, and His524, which can form hydrogen bonds, are calculated. Gaussian 98 software is used and Hartree-Fock theory method, density functional theory method, and nature bond orbital analysis are applied to this study. Because Arg394 moves its position to form more hydrogen bonds to stabilize the structure, the optimized structure is not same with XRD structure.Charge distribution of the structure, and bond length, angle, stabilizing energy (E2), and orbital hybrid of Hydrogen bonds are discussed. Some donor-acceptor bonds are also found in the optimized structure.
For understanding hydrogen bonds in the XRD structure the known coordinates of atoms are fixed in the simplified structure, and only hydrogen atoms are allowed to move, but this constraint can not finish the optimization calculation. If only the relative distance between N and O atoms is fixed, the optimization calculation can be finished, and the result is similar with XRD structure.
To understand if other groups which do not form hydrogen bonds with estrogen affect the combination of estrogen and ER, the whole structure is calculated. The whole structure is divided to two parts, inner is the simplified structure described above and outer is the others. ONIOM method is applied to this calculation and AMBER method is applied to outer part. The bond length and angle of hydrogen bonds are obtained, and future studies will be continued.

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