2-Hydroxyisocaproyl-CoA dehydratase and its activator from Clostridium difficile

FEBS J. 2005 Jan;272(2):550-61. doi: 10.1111/j.1742-4658.2004.04498.x.


The hadBC and hadI genes from Clostridium difficile were functionally expressed in Escherichia coli and shown to encode the novel 2-hydroxyisocaproyl-CoA dehydratase HadBC and its activator HadI. The activated enzyme catalyses the dehydration of (R)-2-hydroxyisocaproyl-CoA to isocaprenoyl-CoA in the pathway of leucine fermentation. The extremely oxygen-sensitive homodimeric activator as well as the heterodimeric dehydratase, contain iron and inorganic sulfur; besides varying amounts of zinc, other metal ions, particularly molybdenum, were not detected in the dehydratase. The reduced activator transfers one electron to the dehydratase concomitant with hydrolysis of ATP, a process similar to that observed with the unrelated nitrogenase. The thus activated dehydratase was separated from the activator and ATP; it catalyzed about 10(4) dehydration turnovers until the enzyme became inactive. Adding activator, ATP, MgCl(2), dithionite and dithioerythritol reactivated the enzyme. This is the first demonstration with a 2-hydroxyacyl-CoA dehydratase that the catalytic electron is recycled after each turnover. In agreement with this observation, only substoichiometric amounts of activator (dehydratase/activator = 10 mol/mol) were required to generate full activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3-Hydroxyacyl CoA Dehydrogenases / genetics
  • 3-Hydroxyacyl CoA Dehydrogenases / metabolism*
  • Adenosine Triphosphatases / metabolism
  • Cloning, Molecular
  • Clostridium difficile / enzymology*
  • Enzyme Activation
  • Fermentation*
  • Leucine / metabolism*


  • 3-Hydroxyacyl CoA Dehydrogenases
  • Adenosine Triphosphatases
  • Leucine