The Molecular Basis of Sulfosugar Selectivity in Sulfoglycolysis

Abstract

The sulfosugar sulfoquinovose (SQ) is produced by essentially all photosynthetic organisms on earth and is metabolized by bacteria through the process of sulfoglycolysis. The sulfoglycolytic Embden-Meyerhof-Parnas pathway metabolises SQ to produce dihydroxyacetone phosphate and sulfolactaldehyde and is analogous to the classical Embden-Meyerhof-Parnas glycolysis pathway for the metabolism of glucose-6-phosphate, though the former only provides one C3 fragment to central metabolism, with excretion of the other C3 fragment as dihydroxypropanesulfonate. Here, we report a comprehensive structural and biochemical analysis of the three core steps of sulfoglycolysis catalyzed by SQ isomerase, sulfofructose (SF) kinase and sulfofructose-1-phosphate (SFP) aldolase. Our data shows that despite the superficial similarity of this pathway to glycolysis, the sulfoglycolytic enzymes are specific for SQ metabolites and are not catalytically active on related metabolites from glycolytic pathways. This observation is rationalized by 3D structures of each enzyme, which reveal the presence of conserved sulfonate-binding pockets. We show that SQ isomerase acts preferentially on the β-anomer of SQ and reversibly produces both SF and sulforhamnose (SR), a previously unknown sugar that acts as a transcriptional regulator for the transcriptional repressor CsqR that regulates SQ-utilization. We also demonstrate that SF kinase is a key regulatory enzyme for the pathway that experiences complex modulation by the metabolites AMP, ADP, ATP, F6P, FBP, PEP, and citrate, and we show that SFP aldolase reversibly synthesizes SFP. This body of work provides fresh insights into the mechanism, specificity and regulation of sulfoglycolysis and has important implications for understanding how this biochemistry interfaces with central metabolism in prokaryotes to process this major repository of biogeochemical sulfur.

Genome sequences of Arthrobacter spp. that use a modified sulfoglycolytic Embden-Meyerhof-Parnas pathway

“…In E. coli these genes encode a transcription factor (CsqR) [15], putative transmembrane proteins for the import of SQ and export of the end-product of the pathway, DHPS (YihO, YihP). The enzymatic steps involve a sulfoquinovosidase (YihQ) for cleavage of SQ glycosides [12], sulfoquinovose mutarotase (YihR) for interconversion of SQ anomers [16], SQ-sulfofructose (SF) isomerase (YihS) that interconverts SQ, SF and sulforhamnose,[6] an ATP-dependent sulfofructose kinase (YihV) that converts SF to SF-1-phosphate (SFP) [6], sulfofructose-1-phosphate aldolase (YihT) which converts SFP to SLA and dihydroxyacetone phosphate [6], and a NADH-dependent sulfolactaldehyde reductase (YihU) to convert SLA to DHPS [17], which is excreted into the growth media ( Fig. 3d ).…”

“…The degradation of sulfoquinovose occurs through pathways of sulfoglycolysis and provides access to its constituent carbon and generates ATP and reducing equivalents (NADH/NADPH) [4]. The sulfoglycolytic Embden-Meyerhof-Parnas (sulfo-EMP) [5, 6], Entner-Doudoroff (sulfo-ED) [7] and sulfofructose transaldolase (sulfo-SFT) [8, 9] pathways cleave the 6-carbon chain of SQ into two 3-carbon fragments, one of which is utilized in primary metabolism, while the other containing the sulfonate group is converted to either sulfolactate (SL) or 2,3-dihydroxypropanesulfonate (DHPS) and excreted. The sulfoglycolytic sulfoquinovose monooxygenase (sulfo-SMO) pathway results in cleavage of the C-S bond of sulfoquinovose and leads to production of glucose, and thus enables the complete breakdown of the SQ molecule [10].…”

A microbial sulfoquinovose monooxygenase pathway that enables sulfosugar assimilation

“…The structural studies highlight key residues in the sulfosugar processing enzymes that have evolved to bind this distinguishing group: an Arg283-Tryp286-H2O(Tyr491) triad for recognition of the sulfonate in the SQase; a Thr220-Gly166-Ser43-H2O(His13-Gln46) cluster for recognition of the sulfonate in the SQGro binding protein; and a proposed binding pocket of Trp206-Arg236-His238-Tyr341-His343 for recognition of sulfonate in the SQ monooxygenase. Well-defined sulfonate binding pockets have been highlighted for the enzymes of the sulfo-EMP pathway 8,21,22 and are useful sequence signatures for bioinformatic studies and assignment of the pathways in unstudied organisms.…”

Oxidative desulfurization pathway for complete catabolism of sulfoquinovose by bacteria

“…Through structural analysis we identified key residues involved in sulfosugar recognition and processing, in order to provide greater confidence to bioinformatic analyses of putative smo gene clusters: an approach that has proven valuable for the identification of tier 1 sulfoglycolytic pathways (8,22,23). This includes the Thr220-Gly166-Ser43-H2O(His13-Gln46) cluster of SmoF for the recognition of SQGro, the Arg283-Tryp286-H2O(Tyr491) triad of SmoI for the recognition of SQGro; and the Trp206-Arg236-His238-Tyr341-His343 constellation of SmoC for the recognition of SQ.…”