title: X-ray crystallography reveals a reduced substrate complex of UDP-galactopyranose mutase poised for covalent catalysis by flavin.
abstract: The flavoenzyme uridine 5'-diphosphate galactopyranose mutase (UGM or Glf) catalyzes the interconversion of UDP-galactopyranose and UDP-galactofuranose. The latter is a key building block for cell wall construction in numerous pathogens, including Mycobacterium tuberculosis. Mechanistic studies of UGM suggested a novel role for the flavin, and we previously provided evidence that the catalytic mechanism proceeds through a covalent flavin-galactose iminium. Here, we describe 2.3 and 2.5 A resolution X-ray crystal structures of the substrate-bound enzyme in oxidized and reduced forms, respectively. In the latter, C1 of the substrate is 3.6 A from the nucleophilic flavin N5 position. This orientation is consistent with covalent catalysis by flavin.
authors.affiliation: Department of Biochemistry, National Magnetic Resonance Facility at Madison, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: Todd D
authors.initials: TD
authors.lastname: Gruber
authors.forename: William M
authors.initials: WM
authors.lastname: Westler
authors.forename: Laura L
authors.initials: LL
authors.lastname: Kiessling
authors.forename: Katrina T
authors.initials: KT
authors.lastname: Forest
mesh_terms: D002384:Catalysis; D018360:Crystallography, X-Ray; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry / Q000378:metabolism*; D019751:Intramolecular Transferases / Q000737:chemistry* / Q000378:metabolism*; D007711:Klebsiella pneumoniae / Q000201:enzymology; D010084:Oxidation-Reduction; D013379:Substrate Specificity
chemical_list: D005182:Flavin-Adenine Dinucleotide; D019751:Intramolecular Transferases; C098051:UDP-galactopyranose mutase