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Biochemistry. 2015 Dec 8;54(48):7142-55. doi: 10.1021/acs.biochem.5b01143. Epub 2015 Nov 24.

Structural Studies of Geosmin Synthase, a Bifunctional Sesquiterpene Synthase with αα Domain Architecture That Catalyzes a Unique Cyclization-Fragmentation Reaction Sequence.

Author information

1
Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania , Philadelphia, Pennsylvania 19104-6323, United States.
2
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory , P.O. Box 20450, Stanford, California 94309, United States.
3
Northeastern Collaborative Access Team/Cornell University, Advanced Photon Source, Argonne National Laboratory , Argonne, Illinois 60439, United States.
4
Department of Chemistry, Brown University , Box H, Providence, Rhode Island 02912-9108, United States.
5
Radcliffe Institute for Advanced Study, Harvard University , Cambridge, Massachusetts 02138, United States.

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.

PMID:
26598179
PMCID:
PMC4674366
DOI:
10.1021/acs.biochem.5b01143
[Indexed for MEDLINE]
Free PMC Article

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