Figure 1.

Rational design of a blue–green photoswitch based on OCP2 modules and the NanoLuc complementation system (split-NLucOCP2). A, Scheme of the light-induced native OCP2 protein dynamics: inactive state (left), called OCP2 orange (OCP2^°), and light-induced active state (right), known as OCP2 red (OCP2^R). The purple line indicates the flexible linker connecting the two domains, the orange line indicates the N-terminal extension. B, NTD and CTD interactions, when expressed as separate peptides, in darkness (left) or under stimulating light. C, In silico prediction of dark OCP2 (top) and dark split-NLucOCP2 (bottom) 3D structures. D, Scheme of the split-NLucOCP2 photoswitch. In the dark, the two OCP2 modules interact with each other, thus bringing the two NanoLuc fragments in proximity and complementing NanoLuc; blue–green light leads to a separation of the two modules, suppressing NanoLuc activity.