Insights into unknown foreign ligand in copper nitrite reductase.

Area of Science:

• Biochemistry
• Enzymology
• Bioinorganic Chemistry

Background:

• Bifunctional copper nitrite reductase (CuNIR) enzymes catalyze two key reactions: nitrite reduction to nitric oxide and dioxygen reduction to hydrogen peroxide.
• The mechanism of nitrite reduction by CuNIR is well-understood, but the oxygen reduction pathway remains largely unknown.
• Studying copper-oxygen complexes is challenging due to their inherent instability, hindering mechanistic investigations.

Purpose of the Study:

• To investigate the unknown oxygen reduction mechanism of copper nitrite reductase (CuNIR).
• To provide spectroscopic and structural evidence for intermediates involved in CuNIR's oxygen reduction pathway.
• To elucidate the role of the catalytic copper site in dioxygen binding and activation.

Main Methods:

• Utilized spectroscopic techniques to probe the catalytic copper (T2Cu) site of CuNIR.
• Determined the structures of CuNIR complexes under reaction conditions.
• Analyzed the binding of a foreign ligand to the T2Cu site.

Main Results:

• Provided spectroscopic evidence for the binding of a foreign ligand to the T2Cu site of CuNIR.
• Determined CuNIR structures that reveal a diatomic molecule bound to the T2Cu site.
• Identified this bound diatomic molecule as potentially representing dioxygen.

Conclusions:

• The study presents the first direct evidence of a diatomic molecule, likely dioxygen, interacting with the catalytic copper site of CuNIR.
• These findings offer crucial insights into the previously uncharacterized oxygen reduction mechanism of CuNIR.
• The identification of this intermediate advances the understanding of copper enzyme catalysis involving oxygen.