Biosynthesis of the earthy odorant geosmin by a bifunctional Streptomyces coelicolor enzyme
Biosynthesis of the earthy odorant geosmin by a bifunctional Streptomyces coelicolor enzyme
复制标题
DOI：
10.1038/nchembio.2007.29
复制
发表时间：
2007-11-01
影响因子：
14.8
通讯作者：
Cane, David E.
中科院分区：
文献类型：
--
作者：
Jiang, Jiaoyang;He, Xiaofei;Cane, David E.
土臭素（1）是潮湿土壤的特征气味以及饮用水和食品中的异味的原因（1），（2）。土臭素是由法呢基二磷酸（FPP，2）通过土壤生物天蓝色链霉菌A3（2）中SCO 6073基因编码的酶产生的（参考文献3）。我们现在已经证明，该蛋白的重组N-末端半部分催化FPP的Mg 2+依赖性环化为germacradienol（3）和germacrene D（4），而高度同源的C-末端结构域，以前被认为是催化沉默的，催化germacradienol的Mg 2+依赖性转化为土臭素。定点诱变证实，N-和C-末端结构域各自具有不同的，独立发挥作用的活性位点。在催化必需的丝氨酸至丙氨酸的germacradienol-土臭素合酶的N-末端结构域中的突变导致FPP转化为倍半萜混合物，其包括鉴定为异epidozene的异常产物（6），其先前被认为是FPP环化为germacradienol的酶结合中间体。
Geosmin (1) is responsible for the characteristic odor of moist soil, as well as off-flavors in drinking water and foodstuffs(1),(2).Geosmin is generated from farnesyl diphosphate (FPP, 2) by an enzyme that is encoded by the SCO6073 gene in the soil organism Streptomyces coelicolor A3 (2) (ref. 3). We have now shown that the recombinant N-terminal half of this protein catalyzes the Mg2+- dependent cyclization of FPP to germacradienol (3) and germacrene D (4), while the highly homologous C-terminal domain, previously thought to be catalytically silent, catalyzes the Mg2+ -dependent conversion of germacradienol to geosmin. Site-directed mutagenesis confirmed that the N- and C-terminal domains each harbor a distinct, independently functioning active site. A mutation in the N- terminal domain of germacradienol-geosmin synthase of a catalytically essential serine to alanine results in the conversion of FPP to a mixture of sesquiterpenes that includes an aberrant product identified as isolepidozene (6), which was previously suggested to be an enzyme-bound intermediate in the cyclization of FPP to germacradienol.