Journal
BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS
Volume 1787, Issue 6, Pages 635-645Publisher
ELSEVIER
DOI: 10.1016/j.bbabio.2009.04.003
Keywords
Electron transfer; Proton transfer; Proton pumping; X-ray crystallography; Membrane protein structure
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The structure of the two-subunit cytochrome c oxidase from Paracoccus denitrificans has been refined using X-ray cryodata to 2.25 angstrom resolution in order to gain further insights into its mechanism of action. The refined structural model shows a number of new features including many additional solvent and detergent molecules. The electron density bridging the heme a(3) iron and Cu-B of the active site is fitted best by a peroxo-group or a chloride ion. Two waters or OH- groups do not fit, one water (or OH-) does not provide sufficient electron density. The analysis of crystals of cytochrome c oxidase isolated in the presence of bromide instead of chloride appears to exclude chloride as the bridging ligand. In the D-pathway a hydrogen bonded chain of six water molecules connects Asn131 and Glu278, but the access for protons to this water chain is blocked by Asn113, Asn131 and Asn199. The K-pathway contains two firmly bound water molecules, an additional water chain seems to form its entrance. Above the hemes a cluster of 13 water molecules is observed which potentially form multiple exit pathways for pumped protons. The hydrogen bond pattern excludes that the Cu-B ligand His326 is present in the imidazolate form. (C) 2009 Elsevier B.V. All rights reserved.
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