Incubation of 2-methylisoborneol synthase with the intermediate analog 2-methylneryl diphosphate
作者:Wayne KW Chou、Colin A Gould、David E Cane
DOI:10.1038/ja.2017.24
日期:2017.5
Incubation of synthetic 2-methylneryl diphosphate (2-MeNPP, 10) with 2-methylisoborneol synthase (MIBS) gave a mixture of products that differed significantly from that derived from the natural substrate (E)-2-methylgeranyl diphosphate (3, 2-MeGPP). The proportion of (-)-2-methylisoborneol (1) decreased from 89 to 17% while that of 2-methylenebornane (4) increased from 10 to 26%, with the relative yields of the isomeric homo-monoterpenes 2-methyl-2-bornene (5) and 1-methylcamphene (6) remaining essentially unchanged (<1% each), as determined by chiral GCâMS analysis. The majority of the product mixture resulting from the MIBS-catalyzed cyclization of 2-MeNPP (10) consisted of the anomalous monocyclic homo-monoterpenes (±)-2-methylllimonene (15, 39%) and 2-methyl-α-terpineol (13, 10%), as well as the acylic derivatives 2-methylnerol (11, 7%) and 2-methyllinalool (14, <1%). The steady-state kinetic parameters of the MIBS-catalyzed reaction, determined using [1-3H]-2-methylneryl diphosphate (2-MeNPP), were kcat 0.0046±0.0003âsâ1, Km 18±6âμm and kcat/Km 2.55 à 102 Mâ1âsâ1. In comparison, the natural substrate 2-MeGPP had a kcat 0.105±0.007âsâ1, Km 95±49âμm and kcat/Km 1.11 à 103 Mâ1âsâ1. Taken together with earlier X-ray crystallographic studies of MIBS, as well as previous investigations of the mechanistically related plant monoterpene cyclase, bornyl diphosphate synthase, these results provide important insights into the binding and cyclization of both native substrates and intermediates and their analogs.
将合成的 2-甲基麦角酰二磷酸酯(2-MeNPP,10)与 2-甲基异龙脑合成酶(MIBS)孵育,得到的混合物产物与天然底物(E)-2-甲基麦角酰二磷酸酯(3,2-MeGPP)得到的产物有很大不同。经手性 GCâMS 分析测定,(-)-2-甲基异龙脑(1)的比例从 89% 降至 17%,而 2-亚甲基龙脑烯(4)的比例从 10% 增至 26%,同分异构体 2-甲基-2-龙脑烯(5)和 1-甲基莰烯(6)的相对产率基本保持不变(均小于 1%)。由 MIBS 催化环化 2-MeNPP (10) 得到的大部分产物混合物由反常的单环同单萜 (±)-2-methylllimonene (15, 39%) 和 2-methyl-α-terpineol (13, 10%) 以及酰基衍生物 2-methylnerol (11, 7%) 和 2-methyllinalool (14, <1%)组成。使用[1-3H]-2-甲基内酰二磷酸(2-MeNPP)测定的MIBS催化反应的稳态动力学参数为:kcat 0.0046±0.0003âsâ1,Km 18±6âμm,kcat/Km 2.55 à 102 Mâ1âsâ1。相比之下,天然底物2-MeGPP的kcat为0.105±0.007âsâ1,Km为95±49âμm,kcat/Km为1.11 à 103 Mâ1âsâ1。结合早先对MIBS的X射线晶体学研究,以及之前对与之有机械相关性的植物单萜烯环化酶--二磷酸冰片酯合成酶的研究,这些结果为了解原生底物和中间体及其类似物的结合和环化提供了重要的启示。