Structural differences between the closed and open states of channelrhodopsin‐2 as observed by EPR spectroscopy

Channelrhodopsin is a cation channel with the unique property of being activated by light. To address structural changes of the open state of the channel, two variants, which contain either 1 or 2 wild‐type cysteines, were derivatised with nitroxide spin label and subjected to electron paramagnetic resonance spectroscopy. Both variants contained the C128T mutation to trap the long‐livedP 3 520state by illumination. Comparison of spin–spin distances in the dark state and after illumination reflect conformational changes in the conductiveP 3 520state involving helices B and F. Spin distance measurements reveal that channelrhodopsin forms a dimer even in the absence of intermolecular N‐terminal cysteines.