Burke Charles, Croteau Rodney
Institute of Biological Chemistry, Program in Plant Physiology, Washington State University, Pullman, Washington 99164-6340, USA.
J Biol Chem. 2002 Feb 1;277(5):3141-9. doi: 10.1074/jbc.M105900200. Epub 2001 Dec 3.
Geranyl diphosphate synthase belongs to a subgroup of prenyltransferases, including farnesyl diphosphate synthase and geranylgeranyl diphosphate synthase, that catalyzes the specific formation, from C(5) units, of the respective C(10), C(15), and C(20) precursors of monoterpenes, sesquiterpenes, and diterpenes. Unlike farnesyl diphosphate synthase and geranylgeranyl diphosphate synthase, which are homodimers, geranyl diphosphate synthase from Mentha is a heterotetramer in which the large subunit shares functional motifs and a high level of amino acid sequence identity (56-75%) with geranylgeranyl diphosphate synthases of plant origin. The small subunit, however, shares little sequence identity with other isoprenyl diphosphate synthases; yet it is absolutely required for geranyl diphosphate synthase catalysis. Coexpression in Escherichia coli of the Mentha geranyl diphosphate synthase small subunit with the phylogenetically distant geranylgeranyl diphosphate synthases from Taxus canadensis and Abies grandis yielded a functional hybrid heterodimer that generated geranyl diphosphate as product in each case. These results indicate that the geranyl diphosphate synthase small subunit is capable of modifying the chain length specificity of geranylgeranyl diphosphate synthase (but not, apparently, farnesyl diphosphate synthase) to favor the production of C(10) chains. Comparison of the kinetic behavior of the parent prenyltransferases with that of the hybrid enzyme revealed that the hybrid possesses characteristics of both geranyl diphosphate synthase and geranylgeranyl diphosphate synthase.
香叶基二磷酸合酶属于异戊二烯基转移酶亚组，包括法尼基二磷酸合酶和香叶基香叶基二磷酸合酶，该亚组催化由C(5)单元特异性形成单萜、倍半萜和二萜各自的C(10)、C(15)和C(20)前体。与同二聚体的法尼基二磷酸合酶和香叶基香叶基二磷酸合酶不同，薄荷中的香叶基二磷酸合酶是一种异源四聚体，其中大亚基与植物来源的香叶基香叶基二磷酸合酶共享功能基序和高水平的氨基酸序列同一性(56 - 75%)。然而，小亚基与其他异戊二烯基二磷酸合酶几乎没有序列同一性；然而它是香叶基二磷酸合酶催化绝对必需的。薄荷香叶基二磷酸合酶小亚基与来自加拿大红豆杉和巨冷杉的系统发育距离较远的香叶基香叶基二磷酸合酶在大肠杆菌中共表达，产生了一种功能性杂交异二聚体，在每种情况下都产生香叶基二磷酸作为产物。这些结果表明，香叶基二磷酸合酶小亚基能够改变香叶基香叶基二磷酸合酶（但显然不是法尼基二磷酸合酶）的链长特异性，以有利于C(10)链的产生。将亲本异戊二烯基转移酶与杂交酶的动力学行为进行比较，发现杂交酶具有香叶基二磷酸合酶和香叶基香叶基二磷酸合酶的特征。
