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Fig. 7 Relevant residues and water molecules in the chromophore environment of three cyan FPs
dsFP483, amFP486, mTFP0.7 and the green FP Dronpa. The coordinates were taken from the
Protein Data Bank, with codes 3CGL [ 86 ], 2A46 [ 87 ], 2OTB [ 88 ], and 2IOV [ 99 ]. The Arginine
residue at position av 96 is omitted for clarity. The av prefix in the residue number refers to the
corresponding position in av GFP after sequence alignment
replaced by Met in Dronpa (see Fig. 7 ) and Ser av 148 by Ala in cmFP512 (this time
with no emptied cavity). 3
The case of the R96M av GFP mutant will be discussed below.
5.1.2 Green Group
In considering the cyan FPs as blueshifted, it is implicitly assumed that the av GFP
chromophore in the gas phase emits green light. Although no emission is detected in
the gas phase [ 62 ], the gas-phase absorption would suggest that it is indeed so.
Somewhat upsetting this picture, Wachter and coworkers pointed out that a very similar arrange-
ment of three H-bond donors would also be present in the immature form of the DsRed protein,
which, however, emits green, not cyan, light [ 86 ]. However, no isolated structure of DsRed with
immature green chromophore is available, the X-ray structures being a mixture of mature and
immature structures.
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