Enzymatic control of dioxygen binding and functionalization of the flavin cofactor

• Published in: Proceedings of the National Academy of Sciences - PNAS 2018-05, Vol.115 (19), p.4909-4914
• Main Authors: Saleem-Batcha, Raspudin, Stull, Frederick, Sanders, Jacob N., Moore, Bradley S., Palfey, Bruce A., Houk, K. N., Teufel, Robin
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - chemistry; Biological Sciences; Catalysis; Coenzymes - chemistry; Cofactors; Crystallography; Crystallography, X-Ray; Dinitrocresols - chemistry; Enzymes; Flavin; Flavonoids; Mimicry; Mixed Function Oxygenases - chemistry; Molecular Docking Simulation; Organic chemistry; Oxidation-Reduction; Oxygen; Oxygen - chemistry; Oxygenation; Physical Sciences; Positioning devices (machinery); Quantum mechanics; Quantum Theory; Substrates; X-ray crystallography
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1801189115

The reactions of enzymes and cofactors with gaseous molecules such as dioxygen (O₂) are challenging to study and remain among the most contentious subjects in biochemistry. To date, it is largely enigmatic how enzymes control and fine-tune their reactions with O₂, as exemplified by the ubiquitous flavin-dependent enzymes that commonly facilitate redox chemistry such as the oxygenation of organic substrates. Here we employ O₂-pressurized X-ray crystallography and quantum mechanical calculations to reveal how the precise positioning of O₂ within a flavoenzyme’s active site enables the regiospecific formation of a covalent flavin–oxygen adduct and oxygenating species (i.e., the flavin-N5-oxide) by mimicking a critical transition state. This study unambiguously demonstrates how enzymes may control the O₂ functionalization of an organic cofactor as prerequisite for oxidative catalysis. Our work thus illustrates how O₂ reactivity can be harnessed in an enzymatic environment and provides crucial knowledge for future rational design of O₂-reactive enzymes.