DOE Synchrotron Light Sources Reveal Structure of Key Enzyme in Metabolism of Carbohydrates

AADase, a 365 kDa homododecameric enzyme that catalyses the conversion of acetoacetate to acetone, is a key component in the anaerobic metabolism of carbohydrate in solventogenic bacteria.

The Science

Acetoacetate decarboxylase is used by bacteria for a critical step in the conversion of starches to alcohols and acetone, a key step in biofuels production.  Now the structure of the enzyme in three dimensions has been solved, allowing scientists to understand the mechanism by which the conver­sion takes place. AADase perturbs the pKa of the nucleophile by means of a desolvation effect by placement of the side chain into the protein core while enforcing the proximity of polar residues, which facilitate decarboxylation through electrostatic and steric effects. This discovery, in turn, will help development of improved enzyme variants through protein engineering, including enzymes that could be used in the production of biofuels. The studies were carried out by a research group based at Boston University using x-ray crystallography stations at the National Synchrotron Light Source and a small angle x-ray scattering station at the Stanford Synchrotron Radiation Lights Source.

BER Program Manager

Amy Swain

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]


Ho, M-C., J.-F. Ménétret, H. Tsuruta and K. N. Allen. 2009. “The Origin of the Electrostatic Perturbation in Acetoacetate Decarboxylase,” Nature 459, 393–7. DOI:10.1038/nature07938.