Second-Coordination-Sphere Effects Reveal Electronic Structure Differences between the Mitochondrial Amidoxime...

Area of Science:

• Biochemistry
• Bioinorganic Chemistry
• Enzymology

Background:

• The human mitochondrial amidoxime reducing component enzyme (hmARC1) plays a crucial role in cellular metabolism.
• Understanding its active site structure and electronic properties is vital for elucidating its catalytic mechanism.

Purpose of the Study:

• To investigate the geometric and electronic structures of hmARC1 in its oxidized and reduced states.
• To understand the enzyme's electronic structure contributions to its reactivity.

Main Methods:

• Combined X-ray absorption and low-temperature electronic absorption spectroscopies.
• Extended X-ray absorption fine structure (EXAFS) analysis.
• Time-dependent density functional theory (TD-DFT) computations.

Main Results:

• The oxidized hmARC1 active site features a 5-coordinate [MoO2(SCys)(PDT)]- structure, with a coordinated cysteine.
• A 5-coordinate geometry is maintained in the reduced state, with protonation of an equatorial oxo group.
• Spectroscopic and computational data revealed distinct electronic properties compared to other sulfite oxidase family enzymes.
• Identified potential π-bonding interactions between the reduced hmARC1 HOMO and substrate LUMO, facilitating oxygen atom transfer.

Conclusions:

• Detailed structural and electronic characterization of hmARC1 in different redox states.
• Elucidation of the mechanism for substrate activation and oxygen atom transfer, involving π-bonding interactions and substrate LUMO occupation.
• Provides a foundation for understanding hmARC1 function and potential therapeutic targeting.