title: Proton transfer in the K-channel analog of B-type Cytochrome c oxidase from Thermus thermophilus.
abstract: A key enzyme in aerobic metabolism is cytochrome c oxidase (CcO), which catalyzes the reduction of molecular oxygen to water in the mitochondrial and bacterial membranes. Substrate electrons and protons are taken up from different sides of the membrane and protons are pumped across the membrane, thereby generating an electrochemical gradient. The well-studied A-type CcO uses two different entry channels for protons: the D-channel for all pumped and two consumed protons, and the K-channel for the other two consumed protons. In contrast, the B-type CcO uses only a single proton input channel for all consumed and pumped protons. It has the same location as the A-type K-channel (and thus is named the K-channel analog) without sharing any significant sequence homology. In this study, we performed molecular-dynamics simulations and electrostatic calculations to characterize the K-channel analog in terms of its energetic requirements and functionalities. The function of Glu-15B as a proton sink at the channel entrance is demonstrated by its rotational movement out of the channel when it is deprotonated and by its high pKA value when it points inside the channel. Tyr-244 in the middle of the channel is identified as the valve that ensures unidirectional proton transfer, as it moves inside the hydrogen-bond gap of the K-channel analog only while being deprotonated. The electrostatic energy landscape was calculated for all proton-transfer steps in the K-channel analog, which functions via proton-hole transfer. Overall, the K-channel analog has a very stable geometry without large energy barriers.
authors.affiliation: Institute of Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany.
authors.forename: Anna Lena
authors.initials: AL
authors.lastname: Woelke
authors.affiliation: Institute of Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany.
authors.forename: Anke
authors.initials: A
authors.lastname: Wagner
authors.affiliation: Institute of Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany.
authors.forename: Gegham
authors.initials: G
authors.lastname: Galstyan
authors.affiliation: Institute of Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany.
authors.forename: Tim
authors.initials: T
authors.lastname: Meyer
authors.affiliation: Institute of Chemistry and Biochemistry, Freie Universität Berlin, Berlin, Germany. Electronic address: knapp@chemie.fu-berlin.de.
authors.forename: Ernst-Walter
authors.initials: EW
authors.lastname: Knapp
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D003576:Electron Transport Complex IV / Q000737:chemistry* / Q000235:genetics; D006860:Hydrogen Bonding; D056004:Molecular Dynamics Simulation; D017494:Proton Pumps / Q000737:chemistry*; D011522:Protons; D012399:Rotation; D055672:Static Electricity; D016963:Thermus thermophilus
chemical_list: D001426:Bacterial Proteins; D017494:Proton Pumps; D011522:Protons; D003576:Electron Transport Complex IV