Structural Characterization of Early Michaelis Complexes in the Reaction Catalyzed by (+)-Limonene Synthase from <i>Citrus sinensis</i> Using Fluorinated Substrate Analogues
作者:Ramasamy P. Kumar、Benjamin R. Morehouse、Jason O. Matos、Karan Malik、Hongkun Lin、Isaac J. Krauss、Daniel D. Oprian
DOI:10.1021/acs.biochem.7b00144
日期:2017.3.28
respectively. The KI values are similar to the KM for the respective nonfluorinated substrates, indicating that fluorine does not significantly perturb binding of the ligand to the enzyme. FGPP and FNPP are also substrates, but with dramatically reduced rates (kcat values of 0.00054 ± 0.00005 and 0.00024 ± 0.00002 s–1, respectively). These data are consistent with a stepwise mechanism for (+)-LS involving ionization
认为单萜合酶反应的立体化学过程是通过选择性结合香叶基二磷酸(GPP)底物的不同构象在反应序列的早期确定的。我们在这里探索使用单氟化底物类似物2-氟-GPP(FGPP)和2-氟神经二磷酸(FNPP)来自柑橘的(+)-柠檬烯合酶[(+)-LS]的早期Michaelis复合物的形成。两者都是为(+)的竞争性抑制剂- LS与ķ我的分别为2.4±0.5和39.5±5.2μM,值。该ķ我值类似于ķ中号对于相应的非氟化底物,表明氟不会显着干扰配体与酶的结合。FGPP和FNPP也是基质,但速率大大降低(k cat值分别为0.00054±0.00005和0.00024±0.00002 s –1, 分别)。这些数据与(+)-LS的逐步机制一致,该逐步机制涉及在限速步骤中将烯丙基GPP底物电离以产生共振稳定的碳正离子。用FGPP和FNPP浸泡apo-(+)-LS晶体,分别获得2.4和2.2Å分辨率的X射线结构。