title: l-Galactose metabolism in Bacteroides vulgatus from the human gut microbiota.
abstract: A previously unknown metabolic pathway for the utilization of l-galactose was discovered in a prevalent 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 (l-galactose dehydrogenase) was determined to oxidize l-galactose to l-galactono-1,5-lactone with kcat and kcat/Km values of 21 s(-1) and 2.0 × 10(5) M(-1) s(-1), respectively. The kinetic product of Bvu0219 is rapidly converted nonenzymatically to the thermodynamically more stable l-galactono-1,4-lactone. Bvu0220 (l-galactono-1,5-lactonase) hydrolyzes both the kinetic and thermodynamic products of 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. In the final step of this pathway, Bvu0222 (l-galactonate dehydrogenase) oxidizes l-galactonate to d-tagaturonate with kcat and kcat/Km values of 0.6 s(-1) and 1.7 × 10(4) M(-1) s(-1), respectively. In the reverse direction, d-tagaturonate is reduced to l-galactonate with values of kcat and kcat/Km of 90 s(-1) and 1.6 × 10(5) M(-1) s(-1), respectively. d-Tagaturonate is subsequently converted to d-glyceraldehyde and pyruvate through enzymes encoded within the degradation pathway for d-glucuronate and d-galacturonate.
authors: Department of Biochemistry and Biophysics, §Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States.
authors: Merlin Eric
authors: ME
authors: Hobbs
authors: Howard J
authors: HJ
authors: Williams
authors: Brandan
authors: B
authors: Hillerich
authors: Steven C
authors: SC
authors: Almo
authors: Frank M
authors: FM
authors: Raushel
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001439:Bacteroides / Q000235:genetics / Q000378:metabolism*; D005690:Galactose / Q000235:genetics / Q000378:metabolism*; D005691:Galactose Dehydrogenases / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007422:Intestines / Q000382:microbiology*; D064307:Microbiota
chemical_list: D001426:Bacterial Proteins; D005691:Galactose Dehydrogenases; C047959:galactose dehydrogenase; D005690:Galactose