Molecular basis of the light-driven switching of the photochromic fluorescent protein Padron.
Reversibly switchable fluorescent proteins can be repeatedly photoswitched between a fluorescent and a nonfluorescent state by irradiation with the light of two different wavelengths. The molecular basis of the switching process remains a controversial topic. Padron0.9 is a reversibly switchable fluorescent protein with "positive" switching characteristics, exhibiting excellent spectroscopic properties. Its chromophore is formed by the amino acids Cys-Tyr-Gly. We obtained high resolution x-ray structures of Padron0.9 in both the fluorescent and the nonfluorescent states and used the structural information for molecular dynamics simulations. We found that in Padron0.9 the chromophore undergoes a cis-trans isomerization upon photoswitching. The molecular dynamics simulations clarified the protonation states of the amino acid residues within the chromophore pocket that influence the protonation state of the chromophore. We conclude that a light driven cis-trans isomerization of the chromophore appears to be the fundamental switching mechanism in all photochromic fluorescent proteins known to date. Distinct absorption cross-sections for the switching wavelengths in the fluorescent and the nonfluorescent state are not essential for efficient photochromism in fluorescent proteins, although they may facilitate the switching process.
Department of NanoBiophotonics, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany.
Tanja
T
Brakemann
Gert
G
Weber
Martin
M
Andresen
Gerrit
G
Groenhof
Andre C
AC
Stiel
Simon
S
Trowitzsch
Christian
C
Eggeling
Helmut
H
Grubmüller
Stefan W
SW
Hell
Markus C
MC
Wahl
Stefan
S
Jakobs
D003460:Crystallization; D018360:Crystallography, X-Ray; D005453:Fluorescence; D005455:Fluorescent Antibody Technique; D008027:Light; D008164:Luminescent Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D010777:Photochemistry; D017785:Photons; D011487:Protein Conformation; D011522:Protons; D013237:Stereoisomerism
D008164:Luminescent Proteins; D011522:Protons