A microbial sulfoquinovose monooxygenase pathway enables sulfosugar assimilation

Breakdown of the sulfosugar sulfoquinovose (SQ, 6-deoxy-6-sulfoglucose), produced by photosynthetic organisms, is an important component of the biogeochemical carbon and sulfur cycles. Here, we reveal a new pathway for SQ degradation involving oxidative desulfurization to release sulfite and complete breakdown of the carbon skeleton of this sugar to support the growth of the plant pathogen Agrobacterium tumefaciens. SQ or its glycoside sulfoquinovosyl glycerol are imported by an ABC transporter system with associated SQ binding protein. A sulfoquinovosidase cleaves the SQ glycoside and a flavin mononucleotide-dependent sulfoquinovose monooxygenase acts in concert with an NADH-dependent flavin reductase to release sulfite and form 6-oxo-glucose. A short-chain dehydrogenase/reductase oxidoreductase reduces 6-oxo-glucose to glucose, allowing it to enter primary metabolism. Structural and biochemical studies provide detailed insights into the binding and recognition of key species along the reaction coordinate. This sulfoquinovose monooxygenase pathway is distributed across alphaproteobacteria and especially within the rhizobiales. This metabolic strategy...