Terpene Cyclases and Prenyltransferases: Structures and Mechanisms of Action

作者：Chun‐Chi Chen, Satish R. Malwal, Xu Han, Weidong Liu, Lixin Ma, Chao Zhai, Longhai Dai, Jian-Wen Huang, Alli Shillo, Janish Desai, Xianqiang Ma, Yonghui Zhang, Rey-Ting Guo, Eric Oldfield · 发表于：ACS Catalysis · 年份：2020 · DOI：10.1021/acscatal.0c04710 · 被引用次数：29 · 研究领域：Plant biochemistry and biosynthesis、Microbial Natural Products and Biosynthesis、Natural product bioactivities and synthesis

Terpenes and isoprenoids are the most diverse small organic molecules on Earth. Here, we obtained the structures of sesquisabinene and santalene synthases from Santalum album L. in the presence or absence of substrate, substrate-like, or product-like molecules for a total of eight structures. All proteins crystallized in an “open”, noncatalytic conformation and, in the case of the FPP structure, three Mg 2+ (MgABC) were bound in the active site region. We found that one of these Mg 2+ (MgB), involved in pocket closure to the catalytically active conformation, interacted with a single inner-sphere amino acid, a bidentate diphosphate, and a facial arrangement of three water molecules, H 2 O- a, b, c: fac- [Mg(H 2 O) 3 XPP(Asn/Asp)]. Paradoxically, the same arrangement of ligands is found in closed-form, catalytically active “head-to-tail” prenyltransferases, such as farnesyl diphosphate synthase (FPPS), leading to the proposal that in these proteins, pocket closure is due to interaction with outer-sphere ligands (typically, two Asps) with H 2 O- a,b . We also discovered an extensive H-bond network that is present in related cyclases and prenyltransferases: the D-motif. This motif is centered around the totally conserved outer-sphere Asp that is bonded via H 2 O- c to MgB and comprises five amino acids, including a very highly conserved residue in the cyclases, an Arg, and a highly conserved residue in the αHT proteins, a Gln, and we propose that this motif may be involved in ca...