Sulfolactaldehyde dehydrogenase of Rhizobium leguminosarum: Kinetic and structural analysis

Sulfolactate (SL) is a short-chain organosulfonate that is an important reservoir of sulfur in the biosphere. SL is produced by oxidation of sulfolactaldehyde (SLA), which in turn derives from sulfoglycolysis of the sulfosugar sulfoquinovose, or through oxidation of 2,3-dihydroxypropanesulfonate. Oxidation of SLA is catalyzed by SLA dehydrogenases belonging to the aldehyde dehydrogenase superfamily. We report that SLA dehydrogenase RlGabD from the sulfoglycolytic bacterium Rhizobium leguminsarum SRDI565 can use both NAD+ and NADP+ as cofactor to oxidize SLA, and indicatively operates through a rapid equilibrium ordered mechanism. We report the cryo-EM structure of RlGabD bound to NADH, revealing a tetrameric quaternary structure and supporting proposal of organosulfonate binding residues in the active site, and a catalytic mechanism. Sequence based homology searches identified SLA dehydrogenase homologs in a range of putative sulfoglycolytic gene clusters in bacteria predominantly from the phyla Actinobacteria, Firmicutes, and Proteobacteria. This work provides a structural and biochemical view of SLA dehydrogenases to complement our knowledge of SLA reductases, and provide detailed insights into a critical step in the organosulfur cycle. Graphical abstractSulfolactate is an important species in the biogeochemical sulfur cycle. Herein we report the 3D cryo-EM structure and kinetics of its biosynthetic enzyme, sulfolactaldehyde dehydrogenase. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=87 SRC="FIGDIR/small/532361v4_ufig1.gif" ALT="Figure 1"> View larger version (18K): org.highwire.dtl.DTLVardef@1f3d1d3org.highwire.dtl.DTLVardef@548615org.highwire.dtl.DTLVardef@12efc0eorg.highwire.dtl.DTLVardef@1a6145c_HPS_FORMAT_FIGEXP M_FIG C_FIG