Acyl-CoA dehydrogenases. A mechanistic overview.

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Acyl-CoA dehydrogenases are flavoproteins catalyzing fatty acid acyl-CoA conjugate dehydrogenation.
• They exhibit diverse substrate specificities but share a common alpha,beta-dehydrogenation mechanism.
• Medium chain acyl-CoA dehydrogenase (MCAD) is a well-studied model for this enzyme class.

Purpose of the Study:

• To elucidate the catalytic mechanism of acyl-CoA dehydrogenases, focusing on MCAD.
• To identify factors governing catalysis, substrate specificity, and electron transfer to electron transferring flavoprotein.
• To detail the roles of hydrogen bonds and active site residues in reaction progression.

Main Methods:

• Mechanistic analysis of medium chain acyl-CoA dehydrogenase.
• Investigation of substrate binding and electronic effects on active site residues.
• Characterization of reaction intermediates, including enzyme-product complexes.

Main Results:

• The alpha,beta-dehydrogenation mechanism involves concerted rupture of substrate alphaC-H and betaC-H bonds.
• Specific hydrogen bonds lower the substrate alphaC-H pKa, while substrate binding raises the active site base (Glu376) pKa.
• A key intermediate is the reduced enzyme-enoyl-CoA complex, facilitating electron transfer to electron transferring flavoprotein.

Conclusions:

• The catalytic efficiency and specificity of acyl-CoA dehydrogenases are finely tuned by active site architecture and substrate interactions.
• Understanding MCAD's mechanism provides insights into the broader family of acyl-CoA dehydrogenases.
• The study highlights the importance of enzyme-bound intermediates in facilitating electron transfer pathways.