Phytochrome photoconversion

Abstract

Tbe spectral properties of native and modified pbytocbromes and the molecular events during phytocbrome pbotoconversion, Pr^^Pfr, are reviewed. Steady-state and time-resolved absorption spectra of native pbytoebrome A, as well as recombinant pbytocbromes (oat and potato pbytoebrome A and potato pbytoebrome B) reconstituted witb pbycocyanobilin and pbytocbromobilin as cbromopbores, are analysed. Tbe vinyl double bond, present at position 18 in pbytocbromobilin and substituted by an etbyl group in pbycocyanobilin, bas a considerable infiuence on tbe pbototransformation kinetics of pbytocbromes A and B, evidently due to a strong interaction of tbis region of tbe cbromopbore witb tbe protein surrounding. Tbe kinetics of tbe pbototransformation of potato pbytoebrome B differs from tbat of oat pbytoebrome A (wild-type and recombinant), indicating tbat tbe cbromophore-protein interaction in pbytoebrome B is different from tbat in pbytoebrome A. It remains to be seen wbetber tbis difference is due to tbe di-versus monoeotyledon origin of tbe pbytocbromes. Optoacoustic spectroscopy, applied to native oat pbytoebrome A, afforded tbermodynamic, structural and kinetic parameters of tbe Pr->l7oo and tbe I7,,,,->Pr pbototransformations. Raman and infrared spectroscopic data for wild-type pbytoebrome A suggest tbat tbe protonated cbromophore in Pr undergoes torsions around two single bonds in addition to tbe Z-^E isomerization of tbe 15,16 double bond, and tbat all transients, possibly witb tbe exception of I,,|, are protonated at tbe central pyrrole ring.

The Structure of Phytochrome: A Picture Is Worth a Thousand Spectra

“…Primary photochemistry is generally accepted to involve a Z-to-E isomerization about the C15,16 double bond (Braslavsky et al, 1997). Consistent with this hypothesis, a recent theoretical study of PCB provided evidence for considerable double-bond character about the C15,16 bond in the ground state but not in the excited state (Gö ller et al, 2005).…”

“…First detected in 1959 by investigators at the USDA Plant Industry Station in Beltsville, MD (Butler et al, 1959), phytochromes share the characteristic that red light (R) irradiation converts the R-absorbing Pr state into the metastable, far-red light (FR)-absorbing Pfr state ( Figure 1B). This photoconversion is reversible, with Pfr returning to Pr either upon absorption of an FR photon or upon prolonged incubation in the dark via a thermal process known as dark reversion (Sineshchekov, 1995;Braslavsky et al, 1997). We now know that this reversible photochemistry reflects the unique environment of a bilin chromophore that is buried within a highly conserved N-terminal photosensory core region.…”

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

“…The capture of a photon of visible light by the phytochrome chromophore occurs within a femtosecond (44). The lightexcited chromophore isomerizes to the Pfr form (45), eventually influencing the structure and surface properties of the phytochrome protein (46).…”

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

“…Red light absorption photoactivates the molecule to form the photoactivated far-red-light absorbing Pfr state (λ max ≈ 702 nm for Cph1) via a series of intermediates (8)(9)(10). 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.…”