Interactions between chromophore and protein in phytochrome identified by novel oxa-, thia- and carba-chromophores.
Six new bilin chromophores of the plant photoreceptor phytochrome have been synthesized, carrying at the photoisomerizing ring D an oxygen or a sulfur atom or a methylene group instead of the pyrrole nitrogen atom. These furanone-, thiophenone- or cyclopentenone-containing compounds bound covalently to the recombinant apophytochrome phyA of Avena sativa. The novel chromoproteins showed hypsochromically shifted absorption spectra with respect to native phytochrome and a strongly diminished photochemical activity, but a three- to four-fold higher fluorescence quantum yield. These results demonstrate that, on the one hand, also ring D-modified chromophores can be forced into a partially extended structure, required for incorporation into the apoprotein binding pocket and covalent binding. On the other hand, the modifications introduced into ring D of the chromophores strongly impede the formation of stable far red-absorbing forms of plant photoreceptor phytochrome (P(fr)-form) of the chromoproteins, highlighting especially the role of the pyrrole nitrogen atom and hydrogen bonding for the precise interactions between that part of the chromophore and the protein for the P(fr)-formation.
Bongards
Christian
C
Max-Planck-Institute for Bioinorganic Chemistry, Mülheim an der Ruhr, Germany.
Gärtner
Wolfgang
W
D001654:Bile Pigments / Q000138:chemical synthesis / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry*; D010834:Phytochrome / Q000737:chemistry*; D011789:Quantum Theory; D011994:Recombinant Proteins / Q000737:chemistry; D013237:Stereoisomerism; D013455:Sulfur / Q000737:chemistry*
D001654:Bile Pigments; D011994:Recombinant Proteins; D010834:Phytochrome; D013455:Sulfur; D002244:Carbon; D010100:Oxygen