Open AccessChannelrhodopsin-2 is a leaky proton pump
Author(s) -
Katrin Feldbauer,
D. Zimmermann,
Verena Pintschovius,
Julia Spitz,
Christian Bamann,
Ernst Bamberg
Publication year - 2009
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - Uncategorized
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.0905852106
Subject(s) - bacteriorhodopsin , ion channel , chemistry , biophysics , halobacterium salinarum , transmembrane domain , voltage clamp , patch clamp , membrane potential , membrane , biochemistry , biology , receptor
Since its discovery, the light-gated cation channel Channelrhodopsin-2 (ChR2) has proven to be a long-sought tool for the noninvasive, light-activated control of neural cells in culture and in living animals. Although ChR2 is widely used in neurobiological applications, little is known about its molecular mechanism. In this work, the unitary conductance of ChR2 was determined for different cations, for example 40 fS at 200 mM NaCl and -60 mV, using noise analysis. The kinetics of the ion channel obtained by noise analysis is in excellent agreement with the photocurrent kinetics obtained by voltage-clamp and time-resolved spectroscopy. The inward rectification of the channel could be explained by the single channel parameters. ChR2 represents an ion channel with a 7 transmembrane helix motif, even though the sequence homology of its essential amino acids to those of the light-driven H(+) pump bacteriorhodopsin (bR) is high. Here, we also show that when ChR2 is expressed in electrofused giant HEK293 cells or reconstituted on planar lipid membranes, it can indeed act as an outwardly driven H(+) pump, demonstrating that ChR2 is bifunctional, and in-line with other microbial rhodopsins, a H(+) pump but with a leak that shows ion channel properties.