Fig. 2

The design of NADH/NAD⁺ sensor SoNar and NADPH sensor iNap. Both SoNar and iNap are cpYFP-based single fluorescent protein sensors. The control sensor iNapc has a similar response to pH as SoNar and iNap but respond to neither NAD(H) or NADPH. For SoNar and iNap, fluorescent protein cpYFP was inserted into a monomer of NAD⁺ (NADH)-binding bacterial protein T-Rex. Binding of NADH (and NAD⁺) and NADPH induces changes in protein conformation and fluorescence of SoNar and iNap sensors, respectively