Sulfoquinovose (SQ) accounts for up to half of the global biosulfur cycle
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The sulfoglycolytic sulfofructose transaldolase pathway enables catabolism of SQ
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2.1-Å cryo-EM structure of the sulfofructose transaldolase Schiff base intermediate
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The catalytic mechanism involves an Asp-Lys-Glu triad
Summary
Sulfoquinovose (SQ) is a key component of plant sulfolipids (sulfoquinovosyl diacylglycerols) and a major environmental reservoir of biological sulfur. Breakdown of SQ is achieved by bacteria through the pathways of sulfoglycolysis. The sulfoglycolytic sulfofructose transaldolase (sulfo-SFT) pathway is used by gut-resident firmicutes and soil saprophytes. After isomerization of SQ to sulfofructose (SF), the namesake enzyme catalyzes the transaldol reaction of SF transferring dihydroxyacetone to 3C/4C acceptors to give sulfolactaldehyde and fructose-6-phosphate or sedoheptulose-7-phosphate. We report the 3D cryo-EM structure of SF transaldolase from Bacillus megaterium in apo and ligand bound forms, revealing a decameric structure formed from two pentameric rings of the protomer. We demonstrate a covalent “Schiff base” intermediate formed by reaction of SF with Lys89 within a conserved Asp-Lys-Glu catalytic triad and defined by an Arg-Trp-Arg sulfonate recognition triad. The structural characterization of the signature enzyme of the sulfo-SFT pathway provides key insights into molecular recognition of the sulfonate group of sulfosugars.
All cryo-EM data have been deposited in the PDB and EM Databank (EMDB) and are publicly available as of the date of publication. Accession numbers are listed in the key resources table. All X-ray diffraction data have been deposited in the PDB and are publicly available as of the date of publication. Accession numbers are listed in the key resources table.
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This paper does not report original code.
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Any additional information required to reanalyse the data reported in this paper is available from the lead contact upon request.
