Fig. 3.

Optical control over GPCR and RTK signaling. (A) The diverse family of G-protein-coupled opsins includes receptors that are activated optimally at different wavelengths of light (colors denote wavelengths mentioned). As shown, the opsins are activated by light from across the visual spectrum. They also selectively activate different families of G proteins as indicated, which can allow optical control over distinct signaling pathways. It is possible to design chimeric opsins that combine the desired spectral tuning and G protein coupling. (B) Light-sensitive RTKs have not been found in nature, but engineered Opto-RTKs can generate the same signaling and cellular responses to those normally triggered by ligands that activate native RTKs. Opto-RTKs consist of RTKs with light-sensitive domains fused to their intracellular region. Photoactivation of these domains causes domain dimerization, resulting in receptor dimerization and activation (orange star).