title: Dammaradiene synthase, a squalene cyclase, from Dryopteris crassirhizoma Nakai.
abstract: Ferns produce a variety of cyclic triterpene hydrocarbons in large amount. Squalene cyclases (SCs) are responsible enzymes for formation of cyclic triterpene hydrocarbon skeletons. Although more than ten bacterial SCs have been cloned and four of them characterized for their enzymatic products, the only example of a fern SC is ACH, from Adiantum capillus-veneris, which produces hydroxyhopane. To obtain a deeper understanding of the molecular evolution of SCs and the origin of the structural diversity of fern triterpenes, further cloning and characterization of SCs have been pursued. In this study, a SC cDNA, DCD, was cloned from Dryopteris crassirhizoma by homology-based RT-PCR. DCD contains a 2058-bp open reading frame that encodes a 685 amino acid polypeptide exhibiting 66% identity to the previously identified fern SC, ACH, and 35-40% identity to bacterial SCs. Heterologous expression of DCD in yeast established it to be a dammaradiene synthase affording dammara-18(28),21-diene, a tetracyclic triterpene hydrocarbon. Although neither this compound nor any derived metabolites have been previously reported from D. crassirhizoma, re-investigation of the leaflets demonstrated the presence of dammara-18(28),21-diene. DCD represents the first SC that produces a tetracyclic triterpene hydrocarbon.
authors.affiliation: Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Junichi
authors.initials: J
authors.lastname: Shinozaki
authors.forename: Masaaki
authors.initials: M
authors.lastname: Shibuya
authors.forename: Kazuo
authors.initials: K
authors.lastname: Masuda
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Ebizuka
mesh_terms: D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D032492:Dryopteris / Q000201:enzymology / Q000235:genetics*; D019143:Evolution, Molecular; D008190:Lyases / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D016366:Open Reading Frames; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018749:RNA, Plant / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013379:Substrate Specificity; D014315:Triterpenes / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D010940:Plant Proteins; D018749:RNA, Plant; D014315:Triterpenes; D008190:Lyases; C022651:squalene cyclase