FTIR studies of phytochrome photoreactions reveal the C=O bands of the chromophore: consequences for its protonation states, conformation, and protein interaction.
The molecular changes of phytochrome during red --> far-red and reverse photoreactions have been monitored by static infrared difference spectroscopy using the recombinant 65 kDa N-terminal fragment assembled with a chromophore chemically modified at ring D or with a chromophore isotopically labeled with (18)O at the carbonyl group of ring A. This allows the identification of the C=O stretching vibrations of rings D and A. We exclude the formation of an iminoether in Pfr. The positions of both these modes show that the chromophore always remains protonated. The upshift of the C=O stretch of ring D in the first photoproducts is explained by a twisted methine bridge connecting rings C and D. The changes in the vibrational pattern during the red --> far-red conversion show that the backreaction is not just the reversal of the forward reaction. The infrared difference spectra of the fragment deviate very little from those of the full-length protein. The differences which are related to the lack of the C-terminal half of the protein constituting the signaling domain are possibly important for the understanding of the signaling mechanism.
Foerstendorf
H
H
Sektion Biophysik, Institut für Molekulare Medizin und Zellforschung, Albert-Ludwigs-Universität, Albertstrasse 23, D-79104 Freiburg, Germany.
Benda
C
C
Gärtner
W
W
Storf
M
M
Scheer
H
H
Siebert
F
F
D018554:Avena / Q000737:chemistry; D015394:Molecular Structure; D010104:Oxygen Radioisotopes / Q000737:chemistry / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010834:Phytochrome / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000378:metabolism; D017550:Spectroscopy, Fourier Transform Infrared
D010104:Oxygen Radioisotopes; D010446:Peptide Fragments; D011994:Recombinant Proteins; D010834:Phytochrome