Journal
BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS
Volume 1807, Issue 7, Pages 769-778Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.bbabio.2010.12.016
Keywords
Heme-copper oxidases; Oxygen binding; Density functional theory (DFT); X-ray refinement
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Funding
- HENAKOTO
- Academy of Finland
- Sigrid Juselius Foundation
- National Graduate School in Informational and Structural Biology
- Academy of Finland through its Centers of Excellence
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Cytochrome c oxidase (CcO) is the terminal enzyme of the respiratory chain. By reducing oxygen to water, it generates a proton gradient across the mitochondrial or bacterial membrane. Recently, two independent Xray crystallographic studies ((Aoyama et al. Proc. Natl. Acad. Sci. USA 106 (2009) 2165-2169) and (Koepke et al. Biochim. Biophys. Acta 1787 (2009) 635-645)), suggested that a peroxide dianion might be bound to the active site of oxidized CcO. We have investigated this hypothesis by combining quantum chemical calculations with a re-refinement of the X-ray crystallographic data and optical spectroscopic measurements. Our data suggest that dianionic peroxide, superoxide, and dioxygen all form a similar superoxide species when inserted into a fully oxidized ferric/cupric binuclear site (BNC). We argue that stable peroxides are unlikely to be confined within the oxidized BNC since that would be expected to lead to bond splitting and formation of the catalytic P intermediate. Somewhat surprisingly, we find that binding of dioxygen to the oxidized binuclear site is weakly exergonic, and hence, the observed structure might have resulted from dioxygen itself or from superoxide generated from O-2 by the X-ray beam. We show that the presence of O-2 is consistent with the X-ray data. We also discuss how other structures, such as a mixture of the aqueous species (H2O + OH- and H2O) and chloride fit the experimental data. (C) 2011 Elsevier B.V. All rights reserved.
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