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revised on 23.09.2020 and posted on 23.09.2020by Mahima Sharma, Palika Abayakoon, Yi Jin, Ruwan Epa, James P. Lingford, Tomohiro Shimada, Masahiro Nakano, Janice Mui, Akira Ishihama, Ethan
D. Goddard-Borger, Gideon J. Davies, Spencer Williams
sulfosugar sulfoquinovose (SQ) is produced by essentially all photosynthetic
organisms on earth and is metabolized 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
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 of these
enzymes, which reveal the presence of conserved sulfonate-binding pockets. We
show that SQ isomerase acts preferentially on the b-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-utilisation. We also demonstrate that SF
kinase is a key regulatory enzyme for the pathway that experiences complex
allosteric modulation by the metabolites AMP, ADP, ATP, F6P, FBP, PEP, and citrate. 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.