Circular Dichroism of the Photoreceptor Pigment Oxyblepharismin

Pieroni, Osvaldo; Plaza, Pascal; Mahet, Mathilde; Angelini, Nicola; Checcucci, Giovanni; Malatesta, Manuela; Martin, Monique M.; Lenci, Francesco

doi:10.1562/2005-04-28-rn-504

Cited by 10 publications

(6 citation statements)

References 21 publications

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“…The very small amplitude of the solvation dynamics is consistent with the weak solvatochromic behavior of OxyBP . The third lifetime, 31 ps, might be compared to a similar weak component observed in the case of free OxyBP in DMSO (15 ps) and previously assigned to a slight change of the nonplanar chiral conformational of the molecule in the excited state. , …”

Section: Discussionsupporting

confidence: 63%

“…14 The third lifetime, 31 ps, might be compared to a similar weak component observed in the case of free OxyBP in DMSO (15 ps 15 ) and previously assigned to a slight change of the nonplanar chiral conformational of the molecule in the excited state. 12,39 As far as dpOxyBP in WCE is concerned, the main excitedstate decay occurs in 4.2 ns. This value is not precisely determined due to our observation window being limited to 1.4 ns.…”

Section: Discussionmentioning

confidence: 99%

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Primary Photoprocesses Involved in the Sensory Protein for the Photophobic Response ofBlepharisma japonicum

et al. 2008

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We present new femtosecond transient-absorption and picosecond fluorescence experiments performed on OBIP, the oxyblepharismin-binding protein believed to trigger the photophobic response of the ciliate Blepharisma japonicum. The formerly identified heterogeneity of the sample is confirmed and rationalized in terms of two independent populations, called rOBIP and nrOBIP. The rOBIP population undergoes a fast photocycle restoring the initial ground state in less than 500 ps. Intermolecular electron transfer followed by electron recombination is identified as the excited-state decay route. The experimental results support the coexistence of the oxyblepharismin (OxyBP) radical cation signature with a stimulated-emission signal at all times of the evolution of the transient-absorption spectra. This observation is interpreted by an equilibrium being reached between the locally excited state and a charge-transfer state on the ground of a theory developed by Mataga and co-workers to explain the fluorescence quenching of aromatic hydrogen-bonded donor-acceptor pairs in nonpolar solvents. OxyBP is supposed to bind to an as yet unknown electron acceptor by a hydrogen-bond (HB) and the coordinate along which forward and backward electron transfer proceed is assumed to be the shift of the HB proton. The observed kinetic isotope effect supports this interpretation. Protein relaxation is finally proposed to accompany the whole process and give rise to the highly multiexponential observed dynamics. As previously reported, the fast photocycle of rOBIP can be interpreted as an efficient sunscreen mechanism that protects Blepharisma japonicum from continuous irradiation. The nrOBIP population, the transient-absorption of which strongly reminds that of free OxyBP in solution, might be proposed to actually trigger the photophobic response of the organism through excited-state deprotonation of the chromophore occurring in the nanosecond regime. Additional femtosecond transient-absorption spectra of OxyBP and peri-deprotonated OxyBP are also reported and used as a comparison basis to interpret the results on OBIP.

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Section: Discussionsupporting

confidence: 63%

Section: Discussionmentioning

confidence: 99%

Primary Photoprocesses Involved in the Sensory Protein for the Photophobic Response ofBlepharisma japonicum

et al. 2008

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“…The very slight differences betweeen the SADS of X 2 and Y 2 should be considered as significant and at the origin of the weak 15-ps component detected in the kinetics. We previously proposed 6,20 that this component reflects an excited-state conformational relaxation of the molecule, a slight change of its nonplanar chiral 32,33 geometry. As for state Z 2 , its difference spectrum is clearly assigned to the triplet state of OxyBP, which we recently published.…”

Section: Oxybp In Dmso Andmentioning

confidence: 98%

Target Analysis of Primary Photoprocesses Involved in the Oxyblepharismin-Binding Protein

Plaza¹,

Mahet²,

Martin³

et al. 2007

J. Phys. Chem. B

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Target analysis is performed on previously published transient absorption spectra of the 200-kDa oxyblepharismin-binding protein (OBIP) thought to trigger the photophobic response of the ciliate Blepharisma japonicum. The OBIP sample is considered as heterogeneous and made of two distinct classes of chromophore-protein complexes. A so-called nonreactive class is seen to be comparable to free oxyblepharismin in organic solution. Another, reactive, class is shown to undergo a fast picosecond photocycle involving the formation in 4 ps of an intermediate state noted Y1. The spectrum associated to Y1 bears striking similarities with that of the oxyblepharismin radical cation. This element favors the hypothesis that an excited-state intermolecular electron-transfer could be the primary step of the sensory transduction chain of B. japonicum. Proton release is also considered as a possible secondary step. These possibilities support the idea that reactive OBIP functions like an electron or proton pump. We alternatively propose a new hypothesis stating that the fast photocycle of reactive OBIP actually does not generate any photoproduct or protein change of conformation but is involved in another biological function. It would act as a kind of solar screen, providing additional protection to the light-adapted form of B. japonicum in case of excessive illumination.

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“…The second lifetime could be compared to a similar weak component observed in the case of free OxyBP in DMSO (15 ps 27 ) and previously assigned to a slight change of the nonplanar chiral conformational of the molecule in the excited state. 2, 25 Most of the overall kinetics is nevertheless accounted for by the 480-ps and step components. These components should be compared to homologous ones found for free OxyBP and the OxyBP:HSA complex.…”

Section: Transient Absorption Spectroscopy Of the Oxybp:bac Complexmentioning

confidence: 99%

“…Such an interaction is indeed supposed to be at work when oxyblepharismin is bound to its native protein partner (the oxyblepharismin-binding protein, OBIP) in lightadapted B. japonicum. [24][25][26][27] We also used partial denaturation of alpha-crystallin (molten globule state 28 ) as a mean to alter the environment of the chromophore bound to alpha-crystallin. Our objective was to probe the excited-state dynamics of OxyBP in interaction with this modified surrounding and compare it to the case of native alpha-crystallin, in order to bring further evidence that the photophysics of the chromophore is controlled by its interaction with the environment.…”

Section: Introductionmentioning

confidence: 99%

Steady-state and femtosecond photoinduced processes of blepharismins bound to alpha-crystallin

Youssef¹,

Brazard²,

Ley³

et al. 2008

Photochem Photobiol Sci

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The interaction of blepharismin (BP) and oxyblepharismin (OxyBP) with bovine alpha-crystallin (BAC) has been studied both by steady-state and femtosecond spectroscopy, with the aim of assessing the possible phototoxicity of these compounds toward the eye tissues. We showed that these pigments form with BAC potentially harmful ground-state complexes, the dissociation constants of which have been estimated to be 6 +/- 2 micromol L(-1) for OxyBP and 9 +/- 4 micromol L(-1) for BP. Irradiation with steady-state visible light of solutions of blepharismins in the presence of BAC proved to induce a quenching of both the pigment and the intrinsic protein fluorescences. These effects were tentatively rationalized in terms of structural changes of alpha-crystallin. On the other hand, femtosecond transient absorption spectroscopy was used to check the occurrence of any type I photoactivity of oxyblepharismin bound to alpha-crystallin. The existence of a particular type of fast photoinduced reaction, not observed in former studies with human serum albumin but present in the natural oxyblepharismin-binding protein, could here be evidenced but no specific reaction was observed during the first few nanoseconds after excitation. Partial denaturation of alpha-crystallin was however found to alter the excited-state behaviour of its complex with oxyblepharismin, making it partly resemble that of free oxyblepharismin in solution.

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Circular Dichroism of the Photoreceptor Pigment Oxyblepharismin

Cited by 10 publications

References 21 publications

Primary Photoprocesses Involved in the Sensory Protein for the Photophobic Response ofBlepharisma japonicum

Primary Photoprocesses Involved in the Sensory Protein for the Photophobic Response ofBlepharisma japonicum

Target Analysis of Primary Photoprocesses Involved in the Oxyblepharismin-Binding Protein

Steady-state and femtosecond photoinduced processes of blepharismins bound to alpha-crystallin

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