Chromophore structure of the physiologically active form (P _fr ) of phytochrome

Abstract

Chromopeptides were prepared by proteolytic digestion of phytochrome (far-red absorbing form, Pfr) and of phycocyanin. The phycocyanobilin peptide, the chromophore of which is Z,Z,Z-configurated, was modified to the Z,ZE isomeric chromophore. It has been demonstrated earlier that the Pfr chromopeptide and the Z,Z,E-configurated phycocyanin chromopeptide behave similarly with regard to spectral and chromatographic properties and reactivity. We present evidence here, obtained by high-resolution 'H NMR spectroscopy, that both the modified phycocyanobilin chromophore and the phytochrome chromophore obtained directly from Pfr are 15E-configurated.Plant development is influenced by light in many ways. An important photoreceptor of higher plants is the chromoprotein phytochrome (1-3), which can mediate light-dependent irreversible differentiation (e.g., seed germination, flowering, and stem and leaf growth) and reversible modulations (e.g., leaflet or chloroplast movement, root tip adhesion, and transmembrane potentials).A characteristic property of phytochrome in vivo (in the plant cell) and in vitro is its photoreversibility. The physiologically inactive (red-absorbing) Pr form (Ama. = 660 nm) is transformed by red light to the physiologically active Pfr form (Amak = 730 nm), which in turn is reconverted by far-red light to the Pr form. nm Pr = Pfr 730 nmThe chemical structure of the Pr chromophore (structure la), including its linkage to the protein, was elucidated by combination of oxidative degradation and UV/visible spectroscopy (4-6), by comparison of the cleaved chromophore with the product obtained by total synthesis (7,8), and by high-resolution NMR spectroscopy of a chromopeptide (9). It is closely related to the structure of the phycocyanin chromophore

Studies on the Structure and Function of Phytochromes as Photoreceptors Based on Synthetic Organic Chemistry

“…It is commonly accepted that the first step in the photoconversion from Pr to Pfr is a Z to E isomerization around the C15=C16 double bond between the C-and D-rings of the bilin chromophores. 28 This photoisomerization generally converts the physiologically inactive red light-absorbing Pr form into the active far-red light-absorbing Pfr form and vice versa. The interchange between the Pr and Pfr forms is essential for light-absorbing biological processes in the phytochrome chromophore function.…”

“…147 Recently, this result was confirmed by X-ray crystallography of a truncated phytochrome from Deinococcus radiodurans consisting of the N-terminal 321 amino acids. For plant phytochromes, it has been shown that the first step of the Pr to Pfr photoconversion is a Z to E isomerization of the chromophore around the C15=C16 double bond, 28 which occurs on the picosecond time scale. [149][150][151] Isomerization is followed by spectral changes in the microsecond and millisecond time scale.…”

“…28 In principle, each exocyclic single bond can adopt either the syn or anti conformation during photoconversion. 16 Vibrational spectroscopy gained indirect insight into the conformation of the phytochrome chromophore in the Pr, Pfr, and intermediate states, but the data were ambiguous and have been interpreted in different ways.…”

Two ground state isoforms and a chromophore D -ring photoflip triggering extensive intramolecular changes in a canonical phytochrome

“…Photoactivation is thought to be initiated by a double bond isomerization of the chromophore (10,11). Early NMR spectroscopic studies on proteolytic phytochrome fragments (12,13) indicated that this isomerization occurs at the C15═C16 double bond (for numbering, see Fig. 1A), a geometrical change in line with vibrational spectroscopic investigations (14)(15)(16) and results from recent 13 C solid-state NMR (17,18) in which the most significant changes during the light-triggered conversions are confined to rings C and D. Exact geometries of the chromophore in the Pr state have been resolved as periplanar ZZZssa configurations in bacteriophytochromes from Deinococcus radiodurans (19) and Rhodopseudomonas palustris (20) as well as in the more plant-phytochrome-like Cph1 from the cyanobacterium Synechocystis 6803 (21).…”

In vitro assembly of phytochrome B apoprotein with synthetic analogs of the phytochrome chromophore

“…11). When the chromophore of phytochrome absorbs the appropriate wavelength of light, a conformational change is induced in both the chromophore and the phytochrome, following a Z to E isomerization at the C15-C16 double bond of the chromophore (12).…”