Structural Basis for Selectivity in Flavin-Dependent Monooxygenase-Catalyzed Oxidative Dearomatization

Journal Article · Mon Mar 25 00:00:00 EDT 2019 · ACS Catalysis

DOI:https://doi.org/10.1021/acscatal.8b04575· OSTI ID:1604206

Rodríguez Benítez, Attabey ^[1]; Tweedy, Sara E. ^[1]; Baker Dockrey, Summer A. ^[1]; Lukowski, April L. ^[1]; Wymore, Troy ^[1]; Khare, Dheeraj ^[1]; Brooks, Charles L. ^[1]; Palfey, Bruce A. ^[1]; Smith, Janet L. ^[1]; Narayan, Alison H. ^[1]

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1. Univ. of Michigan, Ann Arbor, MI (United States)

Biocatalytic reactions embody many features of ideal chemical transformations, including the potential for impeccable selectivity, high catalytic efficiency, mild reaction conditions, and the use of environmentally benign reagents. These advantages have created a demand for biocatalysts that expand the portfolio of complexity-generating reactions available to synthetic chemists. However, the trade-off that often exists between the substrate scope of a biocatalyst and its selectivity limits the application of enzymes in synthesis. We recently demonstrated that a flavin-dependent monooxygenase, TropB, maintains high levels of site- and stereoselectivity across a range of structurally diverse substrates. In this study, we disclose the structural basis for substrate binding in TropB, which performs a synthetically challenging asymmetric oxidative dearomatization reaction with exquisite site- and stereoselectivity across a range of phenol substrates, providing a foundation for future protein engineering and reaction development efforts. Our hypothesis for substrate binding is informed by a crystal structure of TropB and molecular dynamics simulations with the corresponding computational TropB model and is supported by experimental data. In contrast to canonical class A FAD-dependent monooxygenases in which substrates bind in a protonated form, our data indicate that the phenolate form of the substrate binds in the active site. Furthermore, the substrate position is controlled through two-point binding of the phenolate oxygen to Arg206 and Tyr239, which are shown to have distinct and essential roles in catalysis. Arg206 is involved in the reduction of the flavin cofactor, suggesting a role in flavin dynamics. Further, QM/MM simulations reveal the interactions that govern the facial selectivity that leads to a highly enantioselective transformation. Thus, the structural origins of the high levels of site- and stereoselectivity observed in reactions of TropB across a range of substrates are elucidated, providing a foundation for future protein engineering and reaction development efforts.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
• Sponsoring Organization: Graduate Assistance of Areas in National Need (GAANN); National Institutes of Health (NIH); USDOE; Univ. of Michigan Life Sciences Inst.
• OSTI ID: 1604206
• Journal Information: ACS Catalysis, Journal Name: ACS Catalysis Journal Issue: 4 Vol. 9; ISSN 2155-5435
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
crystal structure
flavins
noncovalent interactions
selectivity
surface interactions