Novel thioether bond revealed by a 1.7 A crystal structure of galactose oxidase

Nature. 1991 Mar 7;350(6313):87-90. doi: 10.1038/350087a0.


Galactose oxidase is an extracellular enzyme secreted by the fungus Dactylium dendroides. It is monomeric, with a relative molecular mass of 68,000, catalyses the stereospecific oxidation of a broad range of primary alcohol substrates and possesses a unique mononuclear copper site essential for catalysing a two-electron transfer reaction during the oxidation of primary alcohols to corresponding aldehydes. Recent evidence arguing against a Cu(III)-Cu(I) couple implies the existence of a second redox-active site proposed to involve pyrroloquinoline quinone or a tyrosine radical. We now report the crystal structure of galactose oxidase at 1.7 A resolution. This reveals a unique structural feature at the copper site with a novel thioether bond linking Cys 228 and Tyr 272 in a stacking interaction with Trp 290. We propose that these molecular components stabilize the protein free-radical species essential for catalysis and thus provide a 'built-in' secondary cofactor. This feature may represent a new mechanism for mediating electron transfer in metalloenzymes in the absence of exogenous cofactors.

MeSH terms

  • Binding Sites
  • Chemical Phenomena
  • Chemistry, Physical
  • Copper / chemistry
  • Crystallization
  • Free Radicals
  • Fungi / enzymology
  • Galactose Oxidase / chemistry*
  • Molecular Structure
  • Oxidation-Reduction
  • Protein Conformation
  • Tyrosine
  • X-Ray Diffraction


  • Free Radicals
  • Tyrosine
  • Copper
  • Galactose Oxidase