Sulfur is an essential element for living organisms; the soil-dwelling bacterium Pseudomonas fluorescens, when denied of its typical sources of sulfur, has the ability to convert the organic sulfur compound dimethylsulfone (DMSO2) into sulfite. The reaction pathway by which this happens is in part due to the msu (methanesulfinate utilization) operon that includes two encoded flavin-dependent monooxygenases, MsuC and MsuD. MsuD uses the reduced form of flavin mononucleotide (FMNH-) along with molecular oxygen to convert methanesulfonate to sulfite in the final enzymatic step of the reaction pathway from DMSO2 to sulfite. To further elucidate the mechanism by which MsuD utilizes FMNH- to break the carbon-sulfur bond of methanesulfonate, we report the recombinant protein expression, purification, and crystallography of MsuD and present a structural comparison to homologous monooxygenases from other sulfur assimilation pathways. These results provide structural comparisons that identify protein features responsible for binding of the small substrate, methanesulfonate, in comparison to larger alkyl sulfonates metabolized by homologous monooxygenases.

Structural characterization of MsuD: Flavin-dependent monooxygenase involved in the sulfur assimilation pathway from DMSO<sub>2</sub> of Pseudomonas fluorescens under the sulfur starvation response

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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Structural characterization of MsuD: Flavin-dependent monooxygenase involved in the sulfur assimilation pathway from DMSO2 of Pseudomonas fluorescens under the sulfur starvation response

Structural characterization of MsuD: Flavin-dependent monooxygenase involved in the sulfur assimilation pathway from DMSO₂ of Pseudomonas fluorescens under the sulfur starvation response