title: Kinetics of proton release and uptake by channelrhodopsin-2.
abstract: Electrophysiological experiments showed that the light-activated cation channel channelrhodopsin-2 (ChR2) pumps protons in the absence of a membrane potential. We determined here the kinetics of transient pH change using a water-soluble pH-indicator. It is shown that ChR2 released protons prior to uptake with a stoichiometry of 0.3 protons per ChR2. Comparison to the photocycle kinetics revealed that proton release and uptake match rise and decay of the P(3)(520) intermediate. As the P(3)(520) state also represents the conductive state of cation channeling, the concurrence of proton pumping and channel gating implies an intimate mechanistic link of the two functional modes. Studies on the E123T and S245E mutants show that these residues are not critically involved in proton translocation.
authors.affiliation: Freie Universität Berlin, Institute for Experimental Physics, Berlin, Germany.
authors.forename: Melanie
authors.initials: M
authors.lastname: Nack
authors.forename: Ionela
authors.initials: I
authors.lastname: Radu
authors.forename: Bernd-Joachim
authors.initials: BJ
authors.lastname: Schultz
authors.forename: Tom
authors.initials: T
authors.lastname: Resler
authors.forename: Ramona
authors.initials: R
authors.lastname: Schlesinger
authors.forename: Ana-Nicoleta
authors.initials: AN
authors.lastname: Bondar
authors.forename: Coral
authors.initials: C
authors.lastname: del Val
authors.forename: Stefania
authors.initials: S
authors.lastname: Abbruzzetti
authors.forename: Cristiano
authors.initials: C
authors.lastname: Viappiani
authors.forename: Christian
authors.initials: C
authors.lastname: Bamann
authors.forename: Ernst
authors.initials: E
authors.lastname: Bamberg
authors.forename: Joachim
authors.initials: J
authors.lastname: Heberle
mesh_terms: D001692:Biological Transport; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D017494:Proton Pumps / Q000737:chemistry / Q000378:metabolism*; D011522:Protons; D012243:Rhodopsin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D017494:Proton Pumps; D011522:Protons; D012243:Rhodopsin