The Discovery of New Enzymes in the Human Gut Microbiome

A previously unknown metabolic pathway for the utilization of L‐galactose was discovered in a prevalent human gut bacterium, Bacteroides vulgatus. The new pathway consists of three previously uncharacterized enzymes that were found to be responsible for the conversion of L‐galactose to D‐tagaturonate. Bvu0219 oxidizes L‐galactose to L‐galactono‐1,5‐lactone. However, the kinetic product of the reaction catalyzed by Bvu0219 is converted nonenzymatically to the thermodynamically more stable product, L‐galactono‐1,4‐lactone. The second enzyme, Bvu0220, hydrolyzes both the kinetic and thermodynamic products of the reaction catalyzed by Bvu0219 to L‐galactonate. However, L‐galactono‐1,5‐lactone is estimated to be hydrolyzed 300 fold faster than its thermodynamically more stable counterpart, L‐galactono‐1,4‐lactone. The final enzyme in this pathway, Bvu0222, converts L‐galactonate to D‐tagaturonate. D‐Tagaturonate is subsequently converted to D‐glyceraldehyde and pyruvate through enzymes encoded within the degradation pathway for D‐glucuronate and D‐galacturonate.