Glutaconate CoA-transferase from Acidaminococcus fermentans

Area of Science:

• Biochemistry
• Enzymology
• Microbial Metabolism

Background:

• Glutaconate CoA-transferase facilitates CoA transfer in microbial metabolic pathways.
• Understanding its substrate specificity and reaction mechanism is key to elucidating these pathways.

Purpose of the Study:

• To characterize the substrate specificity and catalytic mechanism of Glutaconate CoA-transferase.
• To purify and determine the structural properties of the enzyme.
• To investigate the enzyme's role in bacterial glutamate fermentation.

Main Methods:

• Enzyme purification from Acidaminococcus fermentans cell-free extracts.
• Substrate specificity assays with various carboxylates and acetyl-CoA.
• Determination of enzyme molecular mass and subunit composition.
• Immunological experiments using antiserum against the transferase.

Main Results:

• The enzyme preferentially accepts (E)-glutaconate but also accepts glutarate, (R)-2-hydroxyglutarate, acrylate, and propionate.
• Reaction with acetyl-CoA and (E)-glutaconate yields the 1-isomer of glutaconyl-CoA; reaction with (R)-2-hydroxyglutarate produces both isomers.
• Purified Glutaconate CoA-transferase has a molecular mass of ~275,000 Da and comprises two polypeptide chains (32,000 and 34,000 Da).
• A thiolester intermediate is formed on the smaller polypeptide chain during catalysis.
• The transferase is essential for glutaconate decarboxylation but not for (R)-2-hydroxyglutarate dehydration.

Conclusions:

• Glutaconate CoA-transferase exhibits broad substrate acceptance and specific isomer formation.
• The enzyme's structure involves distinct polypeptide chains with a catalytic thiolester intermediate.
• The transferase plays a vital role in the metabolic pathway of glutamate fermentation in certain bacteria.