A Widespread Radical-Mediated\nGlycolysis Pathway

Glycyl radical enzymes (GREs) catalyze mechanistically\ndiverse\nradical-mediated reactions, playing important roles in the metabolism\nof anaerobic bacteria. The model bacterium Escherichia\ncoli MG1655 contains two GREs of unknown function,\nYbiW and PflD, which are widespread among human intestinal bacteria.\nHere, we report that YbiW and PflD catalyze ring-opening C–O\ncleavage of 1,5-anhydroglucitol-6-phosphate (AG6P) and 1,5-anhydromannitol-6-phosphate\n(AM6P), respectively. The product of both enzymes, 1-deoxy-fructose-6-phosphate\n(DF6P), is then cleaved by the aldolases FsaA or FsaB to form glyceraldehyde-3-phosphate\n(G3P) and hydroxyacetone (HA), which are then reduced by the NADH-dependent\ndehydrogenase GldA to form 1,2-propanediol (1,2-PDO). Crystal structures\nof YbiW and PflD in complex with their substrates provided insights\ninto the mechanism of radical-mediated C–O cleavage. This “anhydroglycolysis”\npathway enables anaerobic growth of E. coli on 1,5-anhydroglucitol (AG) and 1,5-anhydromannitol (AM), and we\nprobe the feasibility of harnessing this pathway for the production\nof 1,2-PDO, a highly demanded chiral chemical feedstock, from inexpensive\nstarch. Discovery of the anhydroglycolysis pathway expands the known\ncatalytic repertoire of GREs, clarifies the hitherto unknown physiological\nfunctions of the well-studied enzymes FsaA, FsaB, and GldA, and demonstrates\nhow enzyme discovery efforts can cast light on prevalent yet overlooked\nmetabolites in the microbiome.