title: The role of the K-channel and the active-site tyrosine in the catalytic mechanism of cytochrome c oxidase.
abstract: The active site of cytochrome c oxidase (CcO) comprises an oxygen-binding heme, a nearby copper ion (CuB), and a tyrosine residue that is covalently linked to one of the histidine ligands of CuB. Two proton-conducting pathways are observed in CcO, namely the D- and the K-channels, which are used to transfer protons either to the active site of oxygen reduction (substrate protons) or for pumping. Proton transfer through the D-channel is very fast, and its role in efficient transfer of both substrate and pumped protons is well established. However, it has not been fully clear why a separate K-channel is required, apparently for the supply of substrate protons only. In this work, we have analysed the available experimental and computational data, based on which we provide new perspectives on the role of the K-channel. Our analysis suggests that proton transfer in the K-channel may be gated by the protonation state of the active-site tyrosine (Tyr244) and that the neutral radical form of this residue has a more general role in the CcO mechanism than thought previously. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016', edited by Prof. Paolo Bernardi.
authors.affiliation: Department of Physics, Tampere University of Technology, Tampere FI-33101, Finland; Department of Physics, University of Helsinki, Helsinki, Finland. Electronic address: vivek.sharma@tut.fi.
authors.forename: Vivek
authors.initials: V
authors.lastname: Sharma
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki, FI-00014, Finland. Electronic address: marten.wikstrom@helsinki.fi.
authors.forename: Mårten
authors.initials: M
authors.lastname: Wikström
mesh_terms: D000818:Animals; D055162:Biocatalysis; D020134:Catalytic Domain; D002417:Cattle; D003300:Copper / Q000737:chemistry*; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D006418:Heme / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry; D017136:Ion Transport; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D011522:Protons; D014443:Tyrosine / Q000737:chemistry* / Q000378:metabolism
chemical_list: D011522:Protons; D014443:Tyrosine; D006418:Heme; D006639:Histidine; D003300:Copper; D003576:Electron Transport Complex IV
keywords: Electron transfer; Neutral tyrosyl radical; Proton pumping