Functional characterization of recombinant hyoscyamine 6β-hydroxylase from Atropa belladonna
作者:Jing Li、Marco J. van Belkum、John C. Vederas
DOI:10.1016/j.bmc.2012.05.042
日期:2012.7
(-)-Hyoscyamine, the enantiomerically pure form of atropine, and its derivative scopolamine are tropane alkaloids that are extensively used in medicine. Hyoscyamine 6 beta-hydroxylase (H6H, EC 1.14.11.11), a monomeric alpha-ketoglutarate dependent dioxygenase, converts (-)-hyoscyamine to its 6,7-epoxy derivative, scopolamine, in two sequential steps. In this study, H6H of Atropa belladonna (AbH6H) was cloned, heterologously expressed in Escherichia coli, purified and characterized. The catalytic efficiency of AbH6H, especially for the second oxidation, was found to be low, and this may be one of the reasons why Atropa belladonna produces less scopolamine than other species in the same family. 6,7-Dehydrohyoscyamine, a potential precursor for the last step of epoxidation, was shown not to be an obligatory intermediate in the biosynthesis of scopolamine using purified AbH6H with an in vitro O-18 labeling experiment. Moreover, the nitrogen atom in the tropane ring of (-)-hyoscyamine was found to play an important role in substrate recognition. (C) 2012 Elsevier Ltd. All rights reserved.
(-)-东莨菪碱是阿托品的旋光纯形式,而其衍生物天仙子胺是托品烷生物碱的一种,在药物中有着广泛应用。东莨菪碱6β-羟化酶(H6H,EC 1.14.11.11),一种单体α-酮戊二酸依赖型双加氧酶,通过两步连续反应将(-)-东莨菪碱转化为其中间体6,7-环氧衍生物——天仙子胺。本研究中,我们对毒蕈(Atropa belladonna)来源的H6H(AbH6H)进行了克隆、异源表达、纯化及功能表征。实验发现,AbH6H的催化效率较低,尤其是在第二次氧化反应中,这可能是毒蕈相比同属其他物种产生更少天仙子胺的原因之一。潜在的最终环氧化前体——6,7-脱氢东莨菪碱,通过体外O-18标记实验,证实其并非天仙子胺生物合成的必要中间体。此外,托品烷环中的氮原子在底物识别过程中扮演了关键角色。版权 © 2012 Elsevier Ltd. 保留所有权利。