From two to one: resolving CO binding in acetyl-CoA synthase.

Area of Science:

• Bioinorganic Chemistry
• Enzymology
• Spectroscopy

Background:

• Acetyl-CoA synthase (ACS) is crucial for carbon monoxide (CO) fixation into biomolecules.
• Previous low-temperature studies suggested ACS binds two CO ligands in its reduced state (A_red-CO).
• The physiological relevance of the two-CO binding model for ACS remained unconfirmed.

Purpose of the Study:

• To investigate the stoichiometry of CO binding to ACS under near-native, ambient conditions.
• To clarify the coordination state of ACS in its A_red-CO form relevant to biological function.
• To assess the validity of the proposed two-CO ligand model for ACS.

Main Methods:

• Utilized ultrafast and two-dimensional infrared (2D IR) spectroscopy to study ACS.
• Performed experiments under near-native, ambient conditions to mimic physiological environments.
• Complemented spectroscopic data with anharmonic frequency calculations for structural and dynamical insights.

Main Results:

• Demonstrated that Acetyl-CoA synthase binds a single carbon monoxide (CO) ligand under ambient conditions.
• Provided direct spectroscopic evidence clarifying the CO coordination in the A_red-CO state of ACS.
• Contradicted previous low-temperature studies suggesting two CO ligands could bind to ACS.

Conclusions:

• Acetyl-CoA synthase binds only one CO ligand under physiologically relevant, ambient conditions.
• The study clarifies the stoichiometry of CO coordination in ACS, refuting the two-CO model.
• Highlights the power of advanced IR spectroscopy and computational methods for studying bioorganometallic systems.