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Publication Abstract from PubMed

Cytochrome c oxidase (CcO) reduces O2 to water, coupled with a proton-pumping process. The structure of the O2-reduction site of CcO contains two reducing equivalents, Fe a3 (2+) and CuB (1+), and suggests that a peroxide-bound state (Fe a3 (3+)-O(-)-O(-)-CuB (2+)) rather than an O2-bound state (Fe a3 (2+)-O2) is the initial catalytic intermediate. Unexpectedly, however, resonance Raman spectroscopy results have shown that the initial intermediate is Fe a3 (2+)-O(2), whereas Fe a3 (3+)-O(-)-O(-)-CuB (2+) is undetectable. Based on X-ray structures of static non-catalytic CcO forms and mutation analyses for bovine CcO, a proton-pumping mechanism has been proposed. It involves a proton-conducting pathway (the H-pathway) comprising a tandem hydrogen-bond network and a water channel located between the N and P side surfaces. However, a system for unidirectional proton-transport has not been experimentally identified. Here, an essentially identical X-ray structure for the two catalytic intermediates (P and F) of bovine CcO was determined at 1.8 A resolution. A 1.70 A Fe-O distance of the ferryl center could be best described as Fe a3 (4+)=O(2-), not as Fe a3 (4+)-OH(-) The distance suggests a ~800 cm(-1) Raman stretching band. We found an interstitial water molecule which could trigger a rapid proton-coupled electron transfer from tyrosine-OH to the slowly forming Fe a3 (3+)-O(-)-O(-)-CuB (2+) state, preventing its detection, consistent with the unexpected Raman results. The H-pathway structures of both intermediates indicated that during proton-pumping from the hydrogen-bond network to the P-side, a transmembrane helix closes the water channel connecting the N-side with the hydrogen-bond network, facilitating unidirectional proton-pumping during the P-to-F transition.

X-ray structures of catalytic intermediates of cytochrome c oxidase provide insights into its O2-activation and unidirectional proton-pump mechanisms.,Shimada A, Etoh Y, Kitoh-Fujisawa R, Sasaki A, Shinzawa-Itoh K, Hiromoto T, Yamashita E, Muramoto K, Tsukihara T, Yoshikawa S J Biol Chem. 2020 Mar 12. pii: RA119.009596. doi: 10.1074/jbc.RA119.009596. PMID:32165497^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.