title: Converting S-limonene synthase to pinene or phellandrene synthases reveals the plasticity of the active site.
abstract: S-limonene synthase is a model monoterpene synthase that cyclizes geranyl pyrophosphate (GPP) to form S-limonene. It is a relatively specific enzyme as the majority of its products are composed of limonene. In this study, we converted it to pinene or phellandrene synthases after introducing N345A/L423A/S454A or N345I mutations. Further studies on N345 suggest the polarity of this residue plays a critical role in limonene production by stabilizing the terpinyl cation intermediate. If it is mutated to a non-polar residue, further cyclization or hydride shifts occurs so the carbocation migrates towards the pyrophosphate, leading to the production of pinene or phellandrene. On the other hand, mutant enzymes that still possess a polar residue at this position produce limonene as the major product. N345 is not the only polar residue that may stabilize the terpinyl cation because it is not strictly conserved among limonene synthases across species and there are also several other polar residues in this area. These residues could form a "polar pocket" that may collectively play this stabilizing role. Our study provides important insights into the catalytic mechanism of limonene synthases. Furthermore, it also has wider implications on the evolution of terpene synthases.
authors.affiliation: Gene Engineering and Biotechnology Beijing Key Laboratory, College of Life Sciences, Beijing Normal University, Beijing, 100875 China.
authors.forename: Jinkun
authors.initials: J
authors.lastname: Xu
authors.affiliation: Gene Engineering and Biotechnology Beijing Key Laboratory, College of Life Sciences, Beijing Normal University, Beijing, 100875 China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Ai
authors.affiliation: Gene Engineering and Biotechnology Beijing Key Laboratory, College of Life Sciences, Beijing Normal University, Beijing, 100875 China.
authors.forename: Jianhui
authors.initials: J
authors.lastname: Wang
authors.affiliation: Gene Engineering and Biotechnology Beijing Key Laboratory, College of Life Sciences, Beijing Normal University, Beijing, 100875 China.
authors.forename: Jingwei
authors.initials: J
authors.lastname: Xu
authors.affiliation: Gene Engineering and Biotechnology Beijing Key Laboratory, College of Life Sciences, Beijing Normal University, Beijing, 100875 China.
authors.forename: Yongkang
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Gene Engineering and Biotechnology Beijing Key Laboratory, College of Life Sciences, Beijing Normal University, Beijing, 100875 China. Electronic address: yangdong@bnu.edu.cn.
authors.forename: Dong
authors.initials: D
authors.lastname: Yang
mesh_terms: D019757:Carbon-Oxygen Lyases / Q000737:chemistry* / Q000235:genetics; D020134:Catalytic Domain; D053138:Cyclohexenes / Q000737:chemistry; D019753:Intramolecular Lyases / Q000737:chemistry* / Q000235:genetics; D000077222:Limonene; D031337:Mentha spicata / Q000201:enzymology / Q000235:genetics; D008958:Models, Molecular; D016296:Mutagenesis; D009154:Mutation; D011106:Polyisoprenyl Phosphates / Q000737:chemistry; D013729:Terpenes / Q000737:chemistry
chemical_list: D053138:Cyclohexenes; D011106:Polyisoprenyl Phosphates; D013729:Terpenes; C015234:geranyl pyrophosphate; D000077222:Limonene; D019757:Carbon-Oxygen Lyases; C473195:(-)-alpha-pinene synthase; D019753:Intramolecular Lyases; C040265:pinene cyclase I
keywords: Evolution; Limonene; Phellandrene; Pinene; Site-directed mutagenesis; Terpene diversity; Terpene synthase