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          Institute: MPI für Biochemie     Collection: Membrane Biochemistry (D. Oesterhelt)     Display Documents

ID: 39335.0, MPI für Biochemie / Membrane Biochemistry (D. Oesterhelt)
Phytochromes with noncovalently bound chromophores: The ability of apophytochromes to direct tetrapyrrole photoisomerization
Authors:Jorissen, H. J. M. M.; Quest, B.; Lindner, I.; de Marsac, N. T.; Gärtner, W.
Date of Publication (YYYY-MM-DD):2002-05
Title of Journal:Photochemistry and Photobiology
Journal Abbrev.:Photochem. Photobiol.
Issue / Number:5
Start Page:554
End Page:559
Review Status:Peer-review
Audience:Not Specified
Abstract / Description:Chromophore-apoprotein interactions were studied with recombinant apoproteins, oat phytochrome (phyA) and CphB of the cyanobacterium Calothrix PCC7601, which were both incubated with the bilin compounds biliverdin (BV) IXalpha, phycocyanobilin (PCB) and the 3'-methoxy derivative of PCB. Previously it was shown that CphB and its homolog in Calothrix, CphA, show strong sequence similarities with each other and with the phytochromes of higher and lower plants, despite the fact that CphB carries a leucine instead of a cysteine at the chromophore attachment position and thus holds the chromophore only noncovalently. CphA binds tetrapyrrole chromophores in a covalent, phytochrome-like manner. For both cyanobacterial phytochromes, red and far-red light-induced photochemistry has been reported. Thus, the role of the binding site of CphB in directing the photochemistry of noncovalently bound tetrapyrroles was analyzed in comparison with the apoprotein from phyA phytochrome. Both the aforementioned compounds, which were used as chromophores, are not able to form covalent bonds with a phyto chrome-type apoprotein because of their chemical structure (vinyl group at position 3 or methoxy group at position 3'). The BV adducts of both apoproteins showed phytochrome-like photochemistry (formation of red and far-red- absorbing forms of phytochrome [P-r and P-fr forms]). However, incubation of the oat apophytochrome with BV primarily yields a 700 nm form from which the P-r-P-fr, photochemistry can be initiated and to which the system relaxes in the dark after illumination. The results for CphB were compared with a CphB mutant where the chromophore-binding cysteine had been introduced, which, upon incubation with PCB, shows spectral properties nearly identical with its (covalently binding) CphA homolog. A comparison of the spectral properties P-r and P-fr forms) of all the PCB- and BV-containing chromoproteins reveals that the binding site of the cyanobacterial apoprotein is better suited than the plant (oat) phytochrome to noncovalently incorporate the chromophore and to regulate its photochemistry. Our findings support the proposal that the recently identified phytochrome-like prokaryotic photoreceptors, which do not contain a covalently bound chromophore, may trigger a light- induced physiological response.
Comment of the Author/Creator:Date: 2002, MAY
External Publication Status:published
Document Type:Article
Communicated by:N.N.
Affiliations:MPI für Biochemie/Membrane Biochemistry (D. Oesterhelt)
External Affiliations:Max Planck Inst Strahlenchem, Postfach 101365, D-45413 Mulheim,; Germany; Max Planck Inst Strahlenchem, D-45413 Mulheim, Germany; Inst Pasteur, Unite Cyanobacteries, CNRS, URA 2172, Paris, France
Identifiers:ISI:000175490100017 [ID No:1]
ISSN:0031-8655 [ID No:2]
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