Fig. 8 Relevant residues and water molecules in the chromophore environment of av GFP sg11
(F64L/I167T/K238N mutant, displaying very similar optical properties to the original av GFP),
CpYGFP, and EYFP. The coordinates were taken from the Protein Data Bank, with codes 2WUR
[ 100 ], 2DD7 [ 96 ], and 1YFP [ 27 ]. The av prefix in the residue number refers to the corresponding
position in av GFP after sequence alignment
display no such H-bond, its involvement in redshifting was assessed in X-ray
studies on DsRed mutants (see below) [ 45 ].
5.1.4 Neutral Chromophore (GFPn)
While spectral tuning by the protein matrix on the anionic av GFP chromophore
gives rise to a rather broad range of optical properties, the neutral species seems less
tunable, in line with the findings on isolated chromophores in solution [ 57 ] and with
the suppressed contribution of the quinonoid-like resonant structure. The neutral
absorption peak in various av GFP mutants (including the yellow ones) is 400
[ 19 , 97 ], 4 385 nm in mKalama1 (an av GFP mutant [ 89 ]), and 388 nm in Dronpa
4 In av GFP mutants, such as EYFP, featuring the anionic band only, the neutral band emerges by
decreasing the pH below the protein p Ka.