Opto-APCs: Displaying Phytochrome B on the Surface of Living Cells for Optogenetic Studies

Interactions between proteins on the surface of two cells are pivotal in determining cell fate. These might be receptor-ligand pairs or adhesion molecules. Mechanistic and functional details of these interactions can be studied by optogenetics using parts of the photoreceptor phytochrome B (PhyB) of Arabidopsis thaliana. In these cases, PhyB serves as a membrane-bound ligand for engineered receptors or adhesion molecules. Here, we provide a protocol to generate cells that display PhyB as a membrane-bound protein on their surface to serve as the ligand. This is done by expressing a transmembrane SpyCatcher protein on the cells and covalently coupling purified recombinant PhyB-SpyTag to these cells. Coming from immunology, we call the PhyB-coupled cells opto-antigen-presenting cells (opto-APCs).