Photobiophysics and photobiochemistry of the heterogeneous phytochrome system

Sineshchekov, V.A.

doi:10.1016/0005-2728(94)00173-3

Cited by 114 publications

(166 citation statements)

References 243 publications

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“…This barrier is probably caused by a protein-imposed constraint on D ring rotation, thereby affecting the quantum yield. The inverse temperature dependence of P r fluorescence has been used as an argument for the presence of a thermal barrier (Ϸ5 kcal/mol) on the excited-state surface (24). Thus, the Ϸ3-ps I* decay is determined by two parallel decay pathways, one of which inefficiently (Ϸ15%) produces Lumi-R* while the other efficiently reverts to P r .…”

Section: Discussionmentioning

confidence: 99%

Ultrafast excited-state isomerization in phytochrome revealed by femtosecond stimulated Raman spectroscopy

Dasgupta

Frontiera

Taylor

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

193

291

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Photochemical interconversion between the red-absorbing (Pr) and the far-red-absorbing (P fr) forms of the photosensory protein phytochrome initiates signal transduction in bacteria and higher plants. The Pr-to-Pfr transition commences with a rapid Z-to-E photoisomerization at the C 15AC16 methine bridge of the bilin prosthetic group. Here, we use femtosecond stimulated Raman spectroscopy to probe the structural changes of the phycocyanobilin chromophore within phytochrome Cph1 on the ultrafast time scale. The enhanced intensity of the C15-H hydrogen out-of-plane (HOOP) mode, together with the appearance of red-shifted CAC stretch and NOH in-plane rocking modes within 500 fs, reveal that initial distortion of the C 15AC16 bond occurs in the electronically excited I* intermediate. From I*, 85% of the excited population relaxes back to Pr in 3 ps, whereas the rest goes on to the Lumi-R photoproduct consistent with the 15% photochemical quantum yield. The C 15-H HOOP and skeletal modes evolve to a Lumi-R-like pattern after 3 ps, thereby indicating that the C15AC16 Z-to-E isomerization occurs on the excited-state surface.photochemistry ͉ photoisomerization ͉ photosensory proteins ͉ plant signal transduction ͉ time-resolved vibrational spectroscopy L ight sensing and signaling responses mediated by photoreceptors are critical for the survival and growth of all life forms. Phytochromes are a class of biliprotein photoreceptors found in plants, bacteria, and fungi that are capable of sensing red/far-red light via interconversion between red-absorbing (P r ) and far-redabsorbing (P fr ) forms ( Fig. 1) (1). Light absorption by phytochrome triggers a rapid and reversible Z-to-E isomerization of the C 15 AC 16 methine bridge between the C and D rings of its bilin chromophore (2). This photochemistry subsequently drives changes in protein conformation that lead to changes in gene expression that influence growth and development (1, 3). Temporal resolution of the structure of the bilin chromophore during the photoisomerization process is important, not only to unravel common themes underlying ultrafast dynamics of biological reactions, but also for designing synthetic light-harvesting systems with rapid response times, efficient sensing, and energy storage.In the past, ultrafast pump-probe electronic spectroscopy has been used to probe the excited-state dynamics of plant and cyanobacterial (Cph1) phytochromes. Such studies reveal that formation of the isomerized primary photoproduct Lumi-R, characterized by a red-shifted electronic absorption maximum at 700 nm, occurs 25-40 ps after excitation (4-10). The P r excited state exhibits multiexponential fluorescence decay dynamics with at least two lifetimes (10 ps and 45 ps) (5), thereby implicating the presence of at least two excited states. The two-state model for P r * decay has also received support from ultrafast transient absorption measurements on the plant phytochrome phyA, the cyanobacterial phytochrome Cph1, and the bacteriophytochrome Agp1, all of which exhibit two ...

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Section: Discussionmentioning

confidence: 99%

Ultrafast excited-state isomerization in phytochrome revealed by femtosecond stimulated Raman spectroscopy

Dasgupta

Frontiera

Taylor

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

193

291

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“…Moreover, assembly of the closely related bacteriophytochrome Agp1 from Agrobacterium tumefaciens with synthetic, sterically locked biliverdin derivatives (Inomata et al, 2005) strongly supports the conclusion that the Pr chromophore adopts a C15-Z,anti configuration, while the Pfr chromophore assumes a C15-E,anti configuration ( Figure 5). For this reason, as well as the observed bathochromic shift of the primary Lumi-R intermediate (Sineshchekov, 1995), a hula twist about C15 also can be ruled out in the Pr-to-Pfr photoconversion pathway.…”

Section: Light Sensing and Signal Transduction: New Insightsmentioning

confidence: 96%

“…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.…”

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confidence: 99%

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

2005

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“…Photoconversion is known to involve a Z-E isomerization about the C15-C16 double bond of the bilin, as apophytochrome neither photoconverts nor exhibits a typical phytochrome absorbance spectrum (36,94). The exact nature of this chromophore varies for different subfamilies of phytochromes: plant Phys use phytochromobilin (PΦB , Fig 2A), while Cph1s and Cph2s instead utilize phycocyanobilin (PCB).…”

Section: Phytochrome Chromophore Structurementioning

confidence: 99%

Phytochrome Structure and Signaling Mechanisms

Rockwell

Lagarias

2006

Annu. Rev. Plant Biol.

987

1,252

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Phytochromes are a widespread family of red/far-red responsive photoreceptors first discovered in plants, where they constitute one of the three main classes of photomorphogenesis regulators. All phytochromes utilize covalently attached bilin chromophores that enable photoconversion between red-absorbing (P r ) and far-red-absorbing (P fr ) forms. Phytochromes are thus photoswitchable photosensors; canonical phytochromes have a conserved N-terminal photosensory core and a Cterminal regulatory region which typically includes a histidine-kinase-related domain. The discovery of new bacterial and cyanobacterial members of the phytochrome family within the last decade has greatly aided biochemical and structural characterization of this family, with the first crystal structure of a bacteriophytochrome photosensory core appearing in 2005. This structure and other recent biochemical studies have provided exciting new insights into the structure of phytochrome, the photoconversion process that is central to light sensing, and the mechanism of signal transfer by this important family of photoreceptors. Keywordsphytochrome; biochemistry; biliprotein; photoreceptor; light signaling; photochemistry GENERAL INTRODUCTIONPhytochrome was first discovered in plants in 1959 as the photoreceptor that mediates plant growth and development in response to long-wavelength visible light (9). Phytochrome measures the ratio of red light (R) to far-red light (FR), thereby allowing the plant to assess the quantity of photosynthetically active light and trigger shade avoidance responses (89). Phytochromes are found in all flowering plants and cryptophytes, and this important family of developmental regulators constitutes one of the three major classes of photoreceptors in higher plants, with the others being cryptochromes and phototropins (3,8,91). *Corresponding author: Telephone: 530-752-1865; FAX: 530-752-3085; E-mail: jclagarias@ucdavis.edu. SIDE BAR Phytochromes as Sensors of Oxygen-Dependent Heme Catabolism. The bilin chromophores incorporated by all phytochromes are synthesized from heme in two steps. First, a heme oxygenase converts heme into BV, which is directly incorporated as the chromophore of BphP and Fph phytochromes. In plants and cyanobacteria, however, BV is further reduced to yield PΦB in higher plants and PCB in cyanobacteria and green algae. Conversion of BV to PΦB is carried out by HY-2 in the chloroplast, while reduction of BV to yield PCB is instead carried out by PcyA. Both HY-2 and PcyA belong to a conserved family of ferredoxin-dependent bilin reductases. The kinase activity and regulatory signaling state of many phytochromes are regulated not only by light but by the presence or absence of chromophore. The synthesis of chromophore is itself dependent on the heme metabolism of the cell, because chromophore will only be produced sparingly if cells are starved for heme or oxygen. Hence, phytochrome signaling is sensitive to heme metabolism and oxygen levels. Phytochromes therefore integrate both the light en...

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Photobiophysics and photobiochemistry of the heterogeneous phytochrome system

Cited by 114 publications

References 243 publications

Ultrafast excited-state isomerization in phytochrome revealed by femtosecond stimulated Raman spectroscopy

Ultrafast excited-state isomerization in phytochrome revealed by femtosecond stimulated Raman spectroscopy

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

Phytochrome Structure and Signaling Mechanisms

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