Figure 13.

Approximation of nearest neighbor distances between fluorescent proteins. The fluorophore is located on the central α-helix inside the β-can structure. Thus, the fluorophores of two fluorescent proteins are separated by at least 30 Å. Based on the crystal structure of a GFP dimer (pdb 1 GFL, Yang et al., 1996) the distance is 20 Å. The distance was 48 Å in a head to tail arrangement as it is most probably the case for fusion proteins that are frequently applied for FRET standardization.