麩胱甘肽硫轉換酶cGSTM1-1 與不同受質形成複合體之結構及功能 研究
Structure and Functional Study of Glutathione S-transferase cGSTM1-1 Complexed with Various Substrates
中文摘要
研究小雞肝臟的mu 類麩胱甘肽硫轉換酶(glutathione S-transferase) cGSTM1-1，
與麩胱甘肽(GSH)接合上 1,2-epoxy-3-(p-nitrophenoxy) propane (EPNP)形成的 GS- EPNP 作為受質形成複合體，進行 X 光結晶學研究以決定出結構，並修正解析 度至2.8 A。其結構可解釋 cGSTM1-1 中 epoxidase 活性的因素。此複合體在結晶 學上所定義之不對稱單位中含兩個dimer，依序定為 AB 及 CD。在 dimer AB 中，
EPNP 的部分朝向 Arg107 及 Gln165 且形成氫鍵。而在 dimer CD 中，EPNP 的部 分則伸出至由連接b1 及 a1 的 loop 和部分 C 端殘基銜接形成的疏水性區，且 EPNP 上的 phenoxyl ring 與 Trp209 側鏈形成強烈的環堆疊作用。我們因而推論出
此兩種不同構形代表的EPNP 分別接近其啟始及最終催化反應階段，此結論與
cGSTM1-1 突變株的酵素動力學實驗結果相互印證。
英文摘要
We elucidated the three-dimensional structure of mu-class glutathione S-transferase cGSTM1-1 co-crystallized with the glutathionyl conjugated 1,2-epoxy-3-(p-
nitrophenoxy)propane (GS-EPNP) at 2.8A resolution. The product found in the active site was 1-hydroxy-2-(S-glutathionyl)-3- (p-nitrophenoxy) propane, instead of the conventionally decided 2-hydroxy isomer. The structure can explain the epoxidase activity of cGSTM1-1 to the substrates. The EPNP moiety orients towards Arg107(α4 helix), and Gln165(α6 helix ) in dimer AB and protrudes into a hydrophobic region formed by the loop connectingβ1 and α1 and part of the C-terminal tail in dimer CD.
The phenoxyl ring forms strong ring stacking with the Trp209 side-chain in dimer CD. We hypothesize that these two conformations represent the EPNP moiety close to the initial and final stages of the reaction mechanism, respectively. And the
conclusion was confirmed with the report of the mutagenesis and kinetic studies of cGSTM1-1.
