Oral Presentation 2014 International Biophysics Congress

Gating in channelrhodopsin (#25)

Joachim Heberle 1
  1. Freie Universitaet Berlin, Berlin, Germany

The discovery of the light-gated ion channel channelrhodopsin (ChR) set the stage for the novel field of optogenetics where cellular processes are controlled by light. Despite the fact that the crystallographic structure of a ChR chimeric construct was solved (1), the underlying molecular mechanism of light-induced cation permeation in ChR2 remains unknown.  We have traced the structural changes of ChR2 by time-resolved IR spectroscopy, complemented by electrophysiological measurements (2,3). The vibrational changes were resolved across the entire chemical time range (10-14-101 s) including the open states of the channel (P2390 and P3520). Analysis of the amide I vibrations suggests a transient increase in hydration of transmembrane a-helices with t1/2 = 60 ms which tally the onset of cation permeation. We characterized crucial proton transfer steps and found that aspartate 253 accepts the proton released by the Schiff base (t1/2 = 10 ms), the latter being reprotonated by aspartic acid 156 (t1/2 = 2 ms). The internal proton acceptor and donor groups, corresponding to D212 and D115 in bacteriorhodopsin, are clearly different to other microbial rhodopsins indicating that their spatial position in the protein was relocated during evolution. To address structural changes of the channel, ChR2 was subjected to pulsed electron double resonance (pELDOR) spectroscopy (4). Comparison of spin-spin distances in the dark state and after illumination reflect conformational changes in the conductive P3520 state involving helices B and F.

1 2 3 4 

  1. Kato, H.E., Zhang, F., et al., Nature 482 (2012), 369-374
  2. Lórenz-Fonfría, V.A., Resler, et al., Proc. Natl. Acad. Sci. USA 110 (2013), E1273-E1281
  3. Neumann-Verhoefen MK, Neumann K, et al., J. Am. Chem. Soc. 135 (2013), 6968-6976
  4. Krause N, Engelhard C, et al., FEBS Lett. 587 (2013), 3309-3313