Peter Marlies, Yang Yiling, Li Shu-Ming
Institut für Pharmazeutische Biologie und Biotechnologie, Fachbereich Pharmazie, Philipps-Universität Marburg Robert-Koch-Straße 4 35037 Marburg Germany
RSC Adv. 2022 Oct 3;12(43):28171-28177. doi: 10.1039/d2ra05033a. eCollection 2022 Sep 28.
The earthy odor of geosmin with a C skeleton is known from bacteria, fungi and plants. The sesquiterpenoid germacradien-11-ol (germacradienol) is a crucial intermediate in the biosynthesis of geosmin. A bifunctional terpene cyclase for germacradienol formation and its degradation to geosmin had been described in bacteria. Terpene cyclases were also suggested for geosmin formation in basidiomycetes, but not reported for ascomycetes. We identified a putative terpene cyclase in with low sequence homology to N-termini of the bacterial germacradienol/geosmin synthases. Heterologous expression in and biochemical characterization led to the identification of the geosmin precursor germacradienol as the sole detected enzyme product. Germacradienol synthase (GdlS) uses strictly farnesyl diphosphate as substrate for cyclization and requires Mg for its reaction. Multiple sequence alignments with known enzymes indicate the presence of the highly conserved catalytic residues including the DDXXD motif for Mg binding. Phylogenetic analysis suggests different clades of bacterial germacradienol/geosmin synthases and terpene cyclases from fungi.
具有C骨架的土腥味素的泥土气味在细菌、真菌和植物中都有发现。倍半萜类化合物金合欢二烯-11-醇（金合欢二烯醇）是土腥味素生物合成中的关键中间体。一种用于形成金合欢二烯醇并将其降解为土腥味素的双功能萜烯环化酶已在细菌中被描述。也有人提出担子菌中存在用于形成土腥味素的萜烯环化酶，但子囊菌中尚未见报道。我们在[具体物种]中鉴定出一种假定的萜烯环化酶，其与细菌金合欢二烯醇/土腥味素合酶的N端序列同源性较低。在[具体物种]中的异源表达和生化特性鉴定表明，金合欢二烯醇作为土腥味素的前体是唯一检测到的酶产物。金合欢二烯醇合酶（GdlS）严格使用法呢基二磷酸作为环化底物，反应需要Mg。与已知酶的多序列比对表明存在高度保守的催化残基，包括用于结合Mg的DDXXD基序。系统发育分析表明细菌金合欢二烯醇/土腥味素合酶和真菌萜烯环化酶存在不同的进化枝。
