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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
3nm
[
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.
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