Structural Studies of Geosmin Synthase, a Bifunctional Sesquiterpene Synthase with 伪伪 Domain Architecture That Catalyzes a Unique Cyclization鈥揊ragmentation Reaction Sequence

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• 作者：Golda G. Harris ; Patrick M. Lombardi ; Travis A. Pemberton ; Tsutomu Matsui ; Thomas M. Weiss ; Kathryn E. Cole ; Mustafa K枚ksal ; Frank V. Murphy IV ; L. Sangeetha Vedula ; Wayne K. W. Chou ; David E. Cane ; David W. Christianson
• 刊名：Biochemistry
• 出版年：2015
• 出版时间：December 8, 2015
• 年：2015
• 卷：54
• 期：48
• 页码：7142-7155
• 全文大小：668K
• ISSN：1520-4995

文摘

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 (PP_i), 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 伪伪 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 Mg²⁺ 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 Mg²⁺ 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 鈭?6% 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 伪伪 domain architectures as frameworks for bifunctional catalysis.