Structural evolution of the chromophore in the primary stages of trans/cis isomerization in photoactive yellow protein

Karsten Heyne*, Omar F. Mohammed, Anwar Usman, Jens Dreyer, Erik T.J. Nibbering, Michael A. Cusanovich

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

105 Scopus citations


We have studied the structural changes induced by optical excitation of the chromophore in wild-type photoactive yellow protein (PYP) in liquid solution with a combined approach of polarization-sensitive ultrafast infrared spectroscopy and density functional theory calculations. We identify the νC8-C9 marker modes for solution phase PYP in the P and I0 states, from which we derive that the first intermediate state I0 that appears with a 3 ps time constant can be characterized to have a cis geometry. This is the first unequivocal demonstration that the formation of I0 correlates with the conversion from the trans to the cis state. For the P and I0 states we compare the experimentally measured vibrational band patterns and anisotropies with calculations and find that for both trans and cis configurations the planarity of the chromophore has a strong influence. The C7=C8-(C9=O)-S moiety of the chromophore in the dark P state has a trans geometry with the C=O group slightly tilted out-of-plane, in accordance with the earlier reported structure obtained in an X-ray diffraction study of PYP crystals. In the case of I 0, experiment and theory are only in agreement when the C 7=C8-(C9=O)-S moiety has a planar configuration. We find that the carboxylic side group of Glu46 that is hydrogen-bonded to the chromophore phenolate oxygen does not alter its orientation on going from the electronic ground P state, via the electronic excited P* state to the intermediate I0 state, providing conclusive experimental evidence that the primary stages of PYP photoisomerization involve flipping of the enone thioester linkage without significant relocation of the phenolate moiety.

Original languageEnglish (US)
Pages (from-to)18100-18106
Number of pages7
JournalJournal of the American Chemical Society
Issue number51
StatePublished - Dec 28 2005
Externally publishedYes

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry


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