A unique catalytic mechanism for UDP-galactopyranose mutase

Nat Struct Mol Biol. 2004 Jun;11(6):539-43. doi: 10.1038/nsmb772. Epub 2004 May 9.


The flavoenzyme uridine 5'-diphosphate (UDP)-galactopyranose mutase (UGM) catalyzes the interconversion of UDP-galactopyranose (UDP-Galp) and UDP-galactofuranose (UDP-Galf). The latter is an essential precursor to the cell wall arabinogalactan of Mycobacterium tuberculosis. The catalytic mechanism for this enzyme had not been elucidated. Here, we provide evidence for a mechanism in which the flavin cofactor assumes a new role. Specifically, the N5 of the reduced anionic flavin cofactor captures the anomeric position of the galactose residue with release of UDP. Interconversion of the isomers occurs via a flavin-derived iminium ion. To trap this putative intermediate, we treated UGM with radiolabeled UDP-Galp and sodium cyanoborohydride; a radiolabeled flavin-galactose adduct was obtained. Ultraviolet-visible spectroscopy and mass spectrometry indicate that this product is an N5-alkyl flavin. We anticipate that the clarification of the catalytic mechanism for UGM will facilitate the development of anti-mycobacterial agents.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Catalysis
  • Flavins
  • Imines
  • Intramolecular Transferases / chemistry*
  • Intramolecular Transferases / metabolism
  • Isomerism
  • Mass Spectrometry
  • Spectrophotometry, Ultraviolet
  • Uridine Diphosphate / metabolism
  • Uridine Diphosphate Galactose / chemistry
  • Uridine Diphosphate Galactose / metabolism*


  • Flavins
  • Imines
  • Uridine Diphosphate Galactose
  • Uridine Diphosphate
  • Intramolecular Transferases
  • UDP-galactopyranose mutase