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Two radical-dependent mechanisms for anaerobic degradation of the globally abundant organosulfur compound dihydroxypropanesulfonate

Significance DHPS is one of the most abundant organosulfonates on this planet. The mechanisms for DHPS degradation in the anaerobic biosphere are not well understood. Here, we report the bioinformatics-aided discovery, biochemical, and structural characterizations of two O2-sensitive glycyl radical enzymes that use distinct radical-mediated mechanisms for DHPS degradation in anaerobic bacteria from diverse terrestrial and marine sources as well as human gut. These enzymes play an important role in the biogeochemical sulfur cycle and link dietary sulfonates to microbial production of H2S, which is a causative agent of chronic diseases, such as inflammation and colorectal cancer. 2(S)-dihydroxypropanesulfonate (DHPS) is a microbial degradation product of 6-deoxy-6-sulfo-d-glucopyranose (sulfoquinovose), a component of plant sulfolipid with an estimated annual production of 1010 tons. DHPS is also at millimolar levels in highly abundant marine phytoplankton. Its degradation and sulfur recycling by microbes, thus, play important roles in the biogeochemical sulfur cycle. However, DHPS degradative pathways in the anaerobic biosphere are not well understood. Here, we report the discovery and characterization of two O2-sensitive glycyl radical enzymes that use distinct mechanisms for DHPS degradation. DHPS-sulfolyase (HpsG) in sulfate- and sulfite-reducing bacteria catalyzes C–S cleavage to release sulfite for use as a terminal electron acceptor in respiration, producing H2S. DHPS-dehydratase (HpfG), in fermenting bacteria, catalyzes C–O cleavage to generate 3-sulfopropionaldehyde, subsequently reduced by the NADH-dependent sulfopropionaldehyde reductase (HpfD). Both enzymes are present in bacteria from diverse environments including human gut, suggesting the contribution of enzymatic radical chemistry to sulfur flux in various anaerobic niches.