Photoexcitation of the P4480 State Induces a Secondary Photocycle That Potentially Desensitizes Channelrhodopsin-2

• DOI: 10.1021/jacs.8b03931
• Publication Date: 2018-07-23T20:49:50Z
• Authors: Mattia Saita; Franziska Pranga-...; Tom Resler; Ramona Schlesinger; Joachim Heberle; Victor A. Lorenz-...
• Keywords: Neurons; 0301 basic medicine; 0303 health sciences; Light; 500 Naturwissenschaften und Mathematik::530 Physik::530 Physik; photonics; 530; 01 natural sciences; 0104 chemical sciences; Kinetics; 03 medical and health sciences; Channelrhodopsins; photoexcitation; kinetics lasers; light

Channelrhodopsins (ChRs) are light-gated cation channels. In spite of their wide use to activate neurons with light, the photocurrents of ChRs rapidly decay in intensity under both continuous illumination and fast trains of light pulses, broadly referred to as desensitization. This undesirable phenomenon has been explained by two interconnected photocycles, each of them containing a nonconductive dark state (D1 and D2) and a conductive state (O1 and O2). While the D1 and O1 states correspond to the dark-state and P3520 intermediate of the primary all-trans photocycle of ChR2, the molecular identity of D2 and O2 remains unclear. We show that P4480, the last intermediate of the all-trans photocycle, is photoactive. Its photocycle, characterized by time-resolved UV/vis spectroscopy, contains a red-shifted intermediate, I3530. Our results indicate that the D2 and O2 states correspond to the P4480 and I3530 intermediates, connecting desensitization of ChR2 with the photochemical properties of the P4480 intermediate.