Cytochrome c oxidase (CcO) is an enzyme found in the mitochondria that plays a key role in the respiratory chain. It reduces molecular oxygen to water, and this reaction is coupled with proton pumping from the matrix to the intermembrane space. The proton motive force generated by this process drives ATP syntase. Recently, some natural positive regulators of CcO have been reported, and Coiled-coil-helix-coiled-coil-helix domain-containing 2 (CHCHD2) is one of them. CHCHD2 is found in the nucleus and the mitochondrial intermembrane space. It is also known as mitochondrial nuclear retrograde regulator 1 (MNRR), Parkinson's disease 22 (PARK22), and aging-associated gene 10 protein (AAG10). CHCHD2 binds to CcO and enhances the CcO reaction in mitochondria and in vitro. However, the activity enhancement mechanism is unknown. CcO contains CuA, hemea, hemea3 and CuB as its redox center. Hemea is involved in two processes: transferring electrons from CuA to Hemea3 and proton pumping. The binuclear Hemea3-CuB center reduces oxygen. Thus, binding of CHCHD2 to CcO may optimize the structure of these active center and enhance the reaction of CcO. Visible resonance Raman spectra of heme protein including CcO contain many Raman bands from vibrations between atoms composed of heme. These Raman bands sensitively reflect the structural change of Heme. Therefore, we used resonance Raman spectroscopy to compare the active site structure of CcO with and without CHCHD2.
We found that resonance Raman spectra of reduced CcO showed alteration in some bands by CHCHD2 binding such as heme skeletal modes, heme substituents modes, and Fe-His vibrational mode.1 Through 3D mapping analysis, we found that heme substituents involved in the proton pumping pathway were affected by CHCHD2 binding. Based on this result, we proposed that CHCHD2 allosterically optimizes the proton pump pathway and accelerates proton uptake.1