Crystal structure and biochemical characterization of a 3-ketoacyl-CoA thiolase from Ralstoniaeutropha H16

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• ReH16_B0759 is a 3-ketoacyl-coenzyme A (CoA) thiolase from Ralstonia eutropha.
• This enzyme catalyzes a key step in β-oxidation pathways.
• Understanding its structure and function is crucial for metabolic studies.

Purpose of the Study:

• To determine the crystal structures of ReH16_B0759 in apo and CoA-bound forms.
• To elucidate the substrate binding mechanism and catalytic residues.
• To compare its structure and function with the related isozyme ReH16_A1887.

Main Methods:

• X-ray crystallography was used to obtain high-resolution structures.
• Site-directed mutagenesis was employed to confirm catalytic residues.
• Structural comparisons were made between different enzyme forms and isozymes.

Main Results:

• Crystal structures of ReH16_B0759 (apo and CoA-bound) were determined.
• The enzyme functions as a dimer, with monomers containing three subdomains.
• Substrate binding induced minimal structural changes, except for Arg220 movement.
• Conserved residues (Cys89, His347, Cys377) are positioned for catalysis.
• Site-directed mutagenesis confirmed the roles of active site residues.

Conclusions:

• ReH16_B0759 exhibits structural similarity to other degradative thiolases.
• The enzyme binds CoA through hydrogen bonds involving charged residues like Arg220.
• Catalysis likely proceeds via a mechanism conserved among thiolases.
• Unlike ReH16_A1887, ReH16_B0759 does not appear to be involved in complex formation for β-oxidation.