title: Structural Studies of Geosmin Synthase, a Bifunctional Sesquiterpene Synthase with αα Domain Architecture That Catalyzes a Unique Cyclization-Fragmentation Reaction Sequence.
abstract: Geosmin synthase from Streptomyces coelicolor (ScGS) catalyzes an unusual, metal-dependent terpenoid cyclization and fragmentation reaction sequence. Two distinct active sites are required for catalysis: the N-terminal domain catalyzes the ionization and cyclization of farnesyl diphosphate to form germacradienol and inorganic pyrophosphate (PPi), and the C-terminal domain catalyzes the protonation, cyclization, and fragmentation of germacradienol to form geosmin and acetone through a retro-Prins reaction. A unique αα domain architecture is predicted for ScGS based on amino acid sequence: each domain contains the metal-binding motifs typical of a class I terpenoid cyclase, and each domain requires Mg(2+) for catalysis. Here, we report the X-ray crystal structure of the unliganded N-terminal domain of ScGS and the structure of its complex with three Mg(2+) ions and alendronate. These structures highlight conformational changes required for active site closure and catalysis. Although neither full-length ScGS nor constructs of the C-terminal domain could be crystallized, homology models of the C-terminal domain were constructed on the basis of ∼36% sequence identity with the N-terminal domain. Small-angle X-ray scattering experiments yield low-resolution molecular envelopes into which the N-terminal domain crystal structure and the C-terminal domain homology model were fit, suggesting possible αα domain architectures as frameworks for bifunctional catalysis.
authors.affiliation: Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6323, United States.
authors.forename: Golda G
authors.initials: GG
authors.lastname: Harris
authors.affiliation: Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6323, United States.
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Lombardi
authors.affiliation: Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6323, United States.
authors.forename: Travis A
authors.initials: TA
authors.lastname: Pemberton
authors.affiliation: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory , P.O. Box 20450, Stanford, California 94309, United States.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Matsui
authors.affiliation: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory , P.O. Box 20450, Stanford, California 94309, United States.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Weiss
authors.affiliation: Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6323, United States.
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Cole
authors.affiliation: Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6323, United States.
authors.forename: Mustafa
authors.initials: M
authors.lastname: Köksal
authors.affiliation: Northeastern Collaborative Access Team/Cornell University, Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
authors.forename: Frank V
authors.initials: FV
authors.lastname: Murphy
authors.affiliation: Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6323, United States.
authors.forename: L Sangeetha
authors.initials: LS
authors.lastname: Vedula
authors.affiliation: Department of Chemistry, Brown University , Box H, Providence, Rhode Island 02912-9108, United States.
authors.forename: Wayne K W
authors.initials: WK
authors.lastname: Chou
authors.affiliation: Department of Chemistry, Brown University , Box H, Providence, Rhode Island 02912-9108, United States.
authors.forename: David E
authors.initials: DE
authors.lastname: Cane
authors.affiliation: Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6323, United States.|Radcliffe Institute for Advanced Study, Harvard University , Cambridge, Massachusetts 02138, United States.
authors.forename: David W
authors.initials: DW
authors.lastname: Christianson
mesh_terms: D019386:Alendronate / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D018360:Crystallography, X-Ray; D003500:Cyclization; D008274:Magnesium / Q000378:metabolism; D008958:Models, Molecular; D009284:Naphthols / Q000378:metabolism*; D011106:Polyisoprenyl Phosphates / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012717:Sesquiterpenes / Q000378:metabolism*; D048372:Streptomyces coelicolor / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D009284:Naphthols; D011106:Polyisoprenyl Phosphates; D012717:Sesquiterpenes; C515287:germacradienol; C004808:farnesyl pyrophosphate; D008274:Magnesium; C001278:geosmin; D019386:Alendronate