CD spectrum of bacteriorhodopsin

Wu, Shao-Yi; El‐Sayed, Mostafa A.

doi:10.1016/s0006-3495(91)82042-2

Cited by 45 publications

(44 citation statements)

References 20 publications

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“…The discrepancy between our result and those previous reported could be due to either the lower time resolution in the previous work30 (only nanosecond light pulse was used) or the difference in RbR sample preparations. It is noticed that the RbR prepared in our experiments contains small amount of UV-converted form which can be seen from the fine structure of the excitation spectrum of RbR sample.30 Thus, the longer component of the decay of our measurement may be due to the residual UV-converted RbR since the decay lifetime of this form is 19.8 m 3 0 The main decay component (the fast decay component in our curve), however, agrees well with the radiative lifetime of -2.3 ns that can be estimated from the transition moment of the near-UV absorption band of RbR which was reported to be 8.05 D previously 31. Upon the binding of the DAA+ ion to dIRbR, a substantial decrease in the observed fluorescence lifetime is observed.…”

supporting

confidence: 76%

Binding of, and Energy-Transfer Studies from Retinal to, Organic Cations in Regenerated Reduced Bacteriorhodopsin

Wu¹,

El‐Sayed²

1994

J. Phys. Chem.

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Regenerated R b R from deionized R b R (dIRbR) and fluorescent 3,6-diaminoacridine cation (DAA+) is studied as a function of the cation to dIRbR ratio. Using the fluorescence intensity of DAA+, a Scatchard plot was drawn from which two DAA+ are found to be strongly bound while more than three are found to be weakly bound. The retinal in reduced bacteriorhodopsin (RbR) is fluorescent. The fluorescence intensity and decay of the retinal are examined under conditions where there are two strongly bound DAA+ per b R molecule.Assuming that energy transfer between the excited state of the retinal and the DAA+ is responsible for the observed shortening of the retinal excited-state lifetime, the Forster model was used to estimate a donoracceptor distance of 514 A. A discussion of the possible location of the DAA+ with respect to the retinal is given. A comparison between the organic and metal cation binding is made, and a discussion of the possible location of the metal cations in b R is presented.

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supporting

confidence: 76%

Binding of, and Energy-Transfer Studies from Retinal to, Organic Cations in Regenerated Reduced Bacteriorhodopsin

Wu¹,

El‐Sayed²

1994

J. Phys. Chem.

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“…The broader and less intense band in the visible range seen in the bleached sample (curve 2) is from the retinal chromophore, due to its asymmetric conformation (twists in the polyene chain) and/or an asymmetric environment in its binding site. The broad single band of the retinal chromophore, with a maximum at approximately 550 nm, has a shape different from that of bacteriorhodopsin, where a bilobe was observed, associated with the trimeric unit of the purple membrane (Heyn et al 1975 ; Wu and El-Sayed 1991 ). Xanthorhodopsin with bleached salinixanthin, although in the membrane, exhibits a CD spectrum like the spectrum of detergent-solubilized bacteriorhodopsin monomers (Becher and Ebrey 1976 ; Heyn et al 1975 ).…”

Section: Resultsmentioning

confidence: 99%

Removal and Reconstitution of the Carotenoid Antenna of Xanthorhodopsin

et al. 2010

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Salinixanthin, a C40-carotenoid acyl glycoside, serves as a light-harvesting antenna in the retinal-based proton pump xanthorhodopsin of Salinibacter ruber. In the crystallographic structure of this protein, the conjugated chain of salinixanthin is located at the protein–lipid boundary and interacts with residues of helices E and F. Its ring, with a 4-keto group, is rotated relative to the plane of the π-system of the carotenoid polyene chain and immobilized in a binding site near the β-ionone retinal ring. We show here that the carotenoid can be removed by oxidation with ammonium persulfate, with little effect on the other chromophore, retinal. The characteristic CD bands attributed to bound salinixanthin are now absent. The kinetics of the photocycle is only slightly perturbed, showing a 1.5-fold decrease in the overall turnover rate. The carotenoid-free protein can be reconstituted with salinixanthin extracted from the cell membrane of S. ruber. Reconstitution is accompanied by restoration of the characteristic vibronic structure of the absorption spectrum of the antenna carotenoid, its chirality, and the excited-state energy transfer to the retinal. Minor modification of salinixanthin, by reducing the carbonyl C=O double bond in the ring to a C-OH, suppresses its binding to the protein and eliminates the antenna function. This indicates that the presence of the 4-keto group is critical for carotenoid binding and efficient energy transfer.

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“…There are experimental and theoretical studies which propose a twisted structure of the retinal Schiff base in the bR protein environment. The biphasic nature of the CD spectrum of the retinal Schiff base in bR has been explained on the basis of adoption of a twisted structure by the chromophore . In a very recent paper, more evidence for the nonplanarity of the retinal Schiff base structure in the protein environment have been reported after the analysis of the optical rotation of the second harmonic radiation from retinal in bR monomers in Langmuir−Blodgett film .…”

Section: Resultsmentioning

confidence: 99%

Influence of the Methyl Groups on the Structure, Charge Distribution, and Proton Affinity of the Retinal Schiff Base

Tajkhorshid

Suhai

1999

J. Phys. Chem. B

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The effect of the methyl substitutions at different carbon atoms of the polyene chain of the retinal Schiff base has been studied on the structure, charge distribution, and proton affinity (PA) in a Schiff base model with the same number of conjugated double bonds (six conjugated double bonds including the Schiff base group). The methyl groups were added to the nitrogen atom and/or different carbon atoms along the main chain, and the results were compared to those of the retinal Schiff base. To study the effect of the polarization functions on hydrogen atoms, all of the structures were studied using 6-31G* and 6-31G** basis sets at the Becke3LYP (B3LYP) level of theory. For each optimized model, the PA was then calculated on the basis of the difference of the total energy of the protonated and unprotonated species. The influence of the zero-point energy corrections on the PA values was also examined at the same level of theory. The results show that, for all species, the application of the larger basis set (6-31G**) does not significantly influence the structures and the derived charges. Utilization of the larger basis set, however, results in PAs which are, by about 2.0 kcal/mol, systematically higher than the corresponding values obtained from the B3LYP/6-31G* level of theory. The consideration of the thermal energy corrections in the PA calculation, on the other hand, systematically shifts the PA, by about 9.0 kcal/mol, to higher values. The effects of the applied basis set and zero-point energy corrections, therefore, can be neglected in the calculation of the relative PA values. The methyl substitutions have substantial effects on the calculated PA of the studied Schiff base structures. On the basis of the calculated PA values of our models, the presence of at least two methyl groups on the terminal carbon atom of the conjugated chain is of great importance in order to obtain a PA value close to the retinal Schiff base. These groups should be considered in the theoretical studies of the pK a change in this system. The effect of the methyl groups on the overall shape of the chromophore was also found to be significant. These structural features combined with the stabilizing effects of the methyl groups on the positive charge of the main chain potentially influence the isomerization barriers in the retinal Schiff base. Therefore, the location and amount of the twist in the backbone of the chromophore, and consequently the pK a of the Schiff base group, can be manipulated by the protein environment via steric interactions between the methyl groups and the binding pocket of retinal proteins such as bacteriorhodopsin.

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CD spectrum of bacteriorhodopsin

Cited by 45 publications

References 20 publications

Binding of, and Energy-Transfer Studies from Retinal to, Organic Cations in Regenerated Reduced Bacteriorhodopsin

Binding of, and Energy-Transfer Studies from Retinal to, Organic Cations in Regenerated Reduced Bacteriorhodopsin

Removal and Reconstitution of the Carotenoid Antenna of Xanthorhodopsin

Influence of the Methyl Groups on the Structure, Charge Distribution, and Proton Affinity of the Retinal Schiff Base

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