Conformational Flexibility of Phycocyanobilin: An AM1 Semiempirical Study

Göller, Andreas H.; Strehlow, Dietmar; Hermann, Gudrun

doi:10.1002/1439-7641(20011119)2:11<665::aid-cphc665>3.0.co;2-o

Cited by 19 publications

(3 citation statements)

References 15 publications

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“…A second intermediate with red-shifted long-wavelength absorbance maximum and enhanced long-wavelength absorbance intensity appears soon after, followed by a blue-shift of the long-wavelength absorbance maximum concomitant with thioether bond formation. The second intermediate exhibits the spectral signature of a bilin in a more extended conformation with all four nitrogens protonated (18,34,35). 15 N-NMR characterization of the P r state in Cph1 corroborates this interpretation (97).…”

Section: The Structure and Function Of The Phytochrome Photosensory Cmentioning

confidence: 83%

Phytochrome Structure and Signaling Mechanisms

Rockwell

Lagarias

2006

Annu. Rev. Plant Biol.

999

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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Section: The Structure and Function Of The Phytochrome Photosensory Cmentioning

confidence: 83%

Phytochrome Structure and Signaling Mechanisms

Rockwell

Lagarias

2006

Annu. Rev. Plant Biol.

999

1,252

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“…As 1 H-NMR studies reveal, it adopts a cyclic-helical conformation [63] while the structural features that distinguish the other two species, PCB B and PCB C , from PCB A remain unknown. However, semiempirical AM1 studies revealed the coexistence of other most stable cyclic-helical structure and suggested a more stretched conformation for PCB B and PCB C compared to PCB A [70]. However, it remains to be seen whether the structural differences between PCB A , PCB B and PCB C are confined to conformational differences alone or whether they are also due to changes in the protonation state of the tetrapyrrolic ring system [71].…”

Section: Excited-state Dynamics Of Phycocyanobilinmentioning

confidence: 99%

“…The chromophore of phytochrome, phytochromobilin, differs from PCB only by substitution of a vinyl instead of an ethyl group at pyrrole ring D. Thus, PCB is considered to be a suitable model for the phytochrome chromophore. For this reason, the photochemistry and photophysics of PCB has been extensively studied by a series of theoretical and spectroscopic investigations over the past years [63][64][65][66][67][68][69][70][71].…”

Section: Excited-state Dynamics Of Phycocyanobilinmentioning

confidence: 99%

Femtosecond time‐resolved spectroscopy on biological photoreceptor chromophores

Schmitt¹,

Dietzek

Hermann

et al. 2007

Laser & Photonics Reviews

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This paper reviews our results on femtosecond timeresolved spectroscopy (transient absorption, transient-grating and fluorescence spectroscopy) to study the photophysics and photochemistry of the two very important biological photoreceptor chromophores phycocyanobilin (PCB) and protochlorophyllide a (PChla). The compound PCB serves as a model chromophore for the photoreceptor phytochrome. By means of transient-grating spectroscopy where the excitation wavelength was varied over the spectral region of the S0 → S1-absorption the ultrafast processes were studied upon excitation with varying excess energy delivered to the system. On the basis of the results obtained, both the rate of the photoreaction in PCB and the rate of the decay of different excited-state species via different decay channels depend on the excitation wavelength. Furthermore, transient absorption experiments illuminating the excited-state dynamics of PChla, a porphyrin-like compound and, as substrate of the NADPH/protochlorophyllide oxidoreductase (POR), a precursor of the chlorophyll biosynthesis are presented. In addition to pump-energy-dependent measurements performed with PChla dissolved in methanol, the excited-state dynamics of PChla was interrogated in different solvents that were chosen to mimic different environmental conditions. In addition to the femtosecond time-resolved absorption experiments the picosecond time-resolved fluorescence of the system was studied. The transient absorption and time-resolved fluorescence data allow suggesting a detailed model for the excited-state relaxation of PChla describing the excited-state processes in terms of The model suggested to account for the excited-state relaxation processes in protochlorophyllide a upon photoexcitation is presented a branching of the initially excited state population into a reactive and nonreactive path. Thus, the excited-state potential energy surface exhibits two distinct S1 and Sx minima separated from the Franck-Condon region along two most likely orthogonal reaction coordinates. Finally, the model derived is related to models suggested to account for the reduction of PChla to chlorophyllide a within the natural enzymatic environment of POR.

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The Excited‐State Dynamics of Phycocyanobilin in Dependence on the Excitation Wavelength

et al. 2004

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The primary light-induced processes of phycocyanobilin were studied by means of transient-grating spectroscopy, whereby the excitation wavelength was varied over the spectral region of the ground-state absorption. On the basis of the results obtained, both the rate of the photoreaction in phycocyanobilin and the ratio of the decay of different excited-state species via two decay channels depend on the excitation wavelength. Furthermore, the formation of the photoreaction product is also dependent on the pump color. These data support a recently established model for the primary photoprocesses in phycocyanobilin. In addition, phycocyanobilin protonated at the basic pyrrolenine-type nitrogen atom was included in the transient absorption study. The decay behavior was found to be almost unchanged when compared with the unprotonated form, and this suggests that protonation of the tetrapyrrole ring structure has no effect on the overall photochemistry.

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Conformational Flexibility of Phycocyanobilin: An AM1 Semiempirical Study

Cited by 19 publications

References 15 publications

Phytochrome Structure and Signaling Mechanisms

Phytochrome Structure and Signaling Mechanisms

Femtosecond time‐resolved spectroscopy on biological photoreceptor chromophores

The Excited‐State Dynamics of Phycocyanobilin in Dependence on the Excitation Wavelength

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