A structural and biophysical dissection of bacterial sulfoquinovose catabolism

After the amino acids cysteine and methionine, the largest population of organosulfur in the biosphere is as part of the sugar headgroup of sulfoquinovosyl diacylglycerol (SQDG), which is found ubiquitously in photosynthetic membranes in a poorly-understood role. SQDG is composed of a diacylglycerol moiety linked to the sulfosugar sulfoquinovose (SQ). SQ is liberated from SQ by stepwise removal of each acyl chain, then glycosidase action to cleave the C1 glycerol moiety. Following this, SQ is broken down through a range of pathways collectively known as “sulfoglycolysis”, of which 5 distinct variants are known. The first two SQ degradation pathways to be characterized mirror the Entner-Doudoroff and Embden- Meyerhof-Parnas glycolytic pathways in E.coli and P.putida respectively. Both cases they use specific enzymes in an SQ-inducible operon. The third, sulfo-SMO, is found in A.tumefaciens and uses an SQ monooxygenase to enact direct desulfurization of SQ, producing glucose as a final product. The fourth and fifth make use of a central transaldolase (sulfo-TAL) and transketolase (sulfo-TK) respectively.
The goal of this PhD is to characterize, both structurally and biophysically, proteins in the sulfo-SMO pathway in A.tumefaciens and the sulfo-TAL pathway in B.megaterium in order to confirm and analyse their role in SQDG catabolism.