High resolution x-ray structure of tyvelose epimerase from Salmonella typhi

J Biol Chem. 2003 Jun 6;278(23):20874-81. doi: 10.1074/jbc.M301948200. Epub 2003 Mar 17.

Abstract

Tyvelose epimerase catalyzes the last step in the biosynthesis of tyvelose by converting CDP-d-paratose to CDP-d-tyvelose. This unusual 3,6-dideoxyhexose occurs in the O-antigens of some types of Gram-negative bacteria. Here we describe the cloning, protein purification, and high-resolution x-ray crystallographic analysis of tyvelose epimerase from Salmonella typhi complexed with CDP. The enzyme from S. typhi is a homotetramer with each subunit containing 339 amino acid residues and a tightly bound NAD+ cofactor. The quaternary structure of the enzyme displays 222 symmetry and can be aptly described as a dimer of dimers. Each subunit folds into two distinct lobes: the N-terminal motif responsible for NAD+ binding and the C-terminal region that harbors the binding site for CDP. The analysis described here demonstrates that tyvelose epimerase belongs to the short-chain dehydrogenase/reductase superfamily of enzymes. Indeed, its active site is reminiscent to that observed for UDP-galactose 4-epimerase, an enzyme that plays a key role in galactose metabolism. Unlike UDP-galactose 4-epimerase where the conversion of configuration occurs about C-4 of the UDP-glucose or UDP-galactose substrates, in the reaction catalyzed by tyvelose epimerase, the inversion of stereochemistry occurs at C-2. On the basis of the observed binding mode for CDP, it is possible to predict the manner in which the substrate, CDP-paratose, and the product, CDP-tyvelose, might be accommodated within the active site of tyvelose epimerase.

Publication types

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

MeSH terms

  • Binding Sites
  • Cloning, Molecular
  • Crystallography, X-Ray
  • Hexoses / metabolism*
  • Molecular Conformation
  • Protein Structure, Quaternary
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Racemases and Epimerases / chemistry*
  • Racemases and Epimerases / genetics
  • Racemases and Epimerases / metabolism
  • Salmonella typhi / enzymology*
  • UDPglucose 4-Epimerase / chemistry

Substances

  • Hexoses
  • tyvelose
  • Racemases and Epimerases
  • UDPglucose 4-Epimerase

Associated data

  • PDB/10RR