Structural, biophysical, and biochemical insights into C-S bond cleavage by dimethylsulfone monooxygenase.

Sulfur is an essential element for life. Bacteria can obtain sulfur from inorganic sulfate; but in the sulfur starvation-induced response, employ two-component flavin-dependent monooxygenases (TC-FMOs) from the and operons to assimilate sulfur from environmental compounds including alkanesulfonates and dialkylsulfones. Here, we report binding studies of oxidized FMN to enzymes involved within the enzymatic pathway responsible for converting dimethylsulfone (DMSO) to sulfite.

Current understanding of enzyme structure and function in bacterial two-component flavin-dependent desulfonases: Cleaving C-S bonds of organosulfur compounds.

The inherent structural properties of enzymes are critical in defining catalytic function. Often, studies to evaluate the relationship between structure and function are limited to only one defined structural element. The two-component flavin-dependent desulfonase family of enzymes involved in bacterial sulfur acquisition utilize a comprehensive range of structural features to carry out the desulfonation of organosulfur compounds.

Structures of the alkanesulfonate monooxygenase MsuD provide insight into C-S bond cleavage, substrate scope, and an unexpected role for the tetramer.

Bacterial two-component flavin-dependent monooxygenases cleave the stable C-S bond of environmental and anthropogenic organosulfur compounds. The monooxygenase MsuD converts methanesulfonate (MS) to sulfite, completing the sulfur assimilation process during sulfate starvation, but the mechanism of this conversion remains unclear. To explore the mechanism of C-S bond cleavage, we report a series of crystal structures of MsuD from Pseudomonas fluorescens in different liganded states.

Structure and function of the two-component flavin-dependent methanesulfinate monooxygenase within bacterial sulfur assimilation.

Methyl sulfur compounds are a rich source of environmental sulfur for microorganisms, but their use requires redox systems. The bacterial sfn and msu operons contain two-component flavin-dependent monooxygenases for dimethylsulfone (DMSO) assimilation: SfnG converts DMSO to methanesulfinate (MSI), and MsuD converts methanesulfonate (MS) to sulfite. However, the enzymatic oxidation of MSI to MS has not been demonstrated, and the function of the last enzyme of the msu operon (MsuC) is unresolved.

The reduced flavin-dependent monooxygenase SfnG converts dimethylsulfone to methanesulfinate.

The biochemical pathway through which sulfur may be assimilated from dimethylsulfide (DMS) is proposed to proceed via oxidation of DMS to dimethylsulfoxide (DMSO) and subsequent conversion of DMSO to dimethylsulfone (DMSO2). Analogous chemical oxidation processes involving biogenic DMS in the atmosphere result in the deposition of DMSO2 into the terrestrial environment. Elucidating the enzymatic pathways that involve DMSO2 contribute to our understanding of the global sulfur cycle.