Figure 1.

Common principles of biosensors designed to measure cAMP and cGMP. (a) Cyclic nucleotides can be monitored by directly measuring cyclic nucleotide gated channel (CNGC) currents or calcium influx through these channels by a calcium sensitive dye; (b) FRET sensors can be constructed based on the fluorophore-labeled protein kinase A (PKA) heterotetramer (R and C subunits), partially truncated protein kinase G (PKG) or single cAMP or cGMP binding domains; (c) Single circularly permuted cpGFP fused to cGMP binding sites from PKG can be used as a sensor for cGMP termed FlincG; (d,e) BRET biosensors use similar parts of proteins fused to Rluc and GFP.