Optical switches for remote and noninvasive control of cell signaling

Abstract

Although the identity and interactions of signaling proteins have been studied in great detail, the complexity of signaling networks cannot be fully understood without elucidating the timing and location of activity of individual proteins. To do this, one needs a means for detecting and controlling specific signaling events. An attractive approach is to use light, both to report on and control signaling proteins in cells, because light can probe cells in real time with minimal damage. Although optical detection of signaling events has been successful for some time, the development of the means for optical control has accelerated only recently. Of particular interest is the development of chemically engineered proteins that are directly sensitive to light.

Fig. 1.

Strategies for the manipulation of cell signaling with light. (A) Uncaging of ligands and ions (9, 37). (B) Protein uncaging. (C) Free photoisomerizable ligands (10, 11). (D) Light-gated cation channel Channelrhodopsin 2 (38). (E) Light-gated chloride pump NpHR (16). (F) PAC (20). ATP, adenosine triphosphate; cAMP, adenosine 3′,5′-monophosphate. (G) Light-gated mechanosensitive channel McsL (22). The asterisk indicates delivery of chemical. (H) Light-gated nAChR (10) and LiGluR (33). (I) Light-gated voltage-gated potassium channel (31).

Fig. 2.

Azobenzene photoisomerizes between an extended or trans configuration under visible light (left) and a bent or cis configuration under UV light (right), which is shorter by ~0.7 nm. Δ indicates thermal energy.

Fig. 3.

Spatio-temporal control of cell signaling with light. (A) The use of spatially confined illumination on a group of cells expressing a photoswitchable protein allows selection of the particular cell (or cell region) to be manipulated. (B) LiGluR allows control of single action potential firing in neurons by millisecond light pulses. [Reproduced with permission from (35)]. (C) Region-selective conjugation of synthetic photoswitches using affinity labeling (34).