Unique biphasic band shape of the visible circular dichroism of bacteriorhodopsin in purple membrane

Cassim, Joseph Y.

doi:10.1016/s0006-3495(92)81701-0

Cited by 43 publications

(59 citation statements)

References 54 publications

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“…Chemical treatment seems to increase membrane fluidity. These changes would bring about a change in lattice vibrations [17]. Another important feature of the CD of D85N is that the maximum of the CD band is 30 nm shorter than the absorption maximum.…”

Section: Resultsmentioning

confidence: 99%

Trimeric mutant bacteriorhodopsin, D85N, shows a monophasic CD spectrum

et al. 1993

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The structure of mutant bacteriorhodopsin (bR), D85N, was examined by CD and X-ray diffraction at pH 7. The absorption maximum of D85N at pH 7 is located at 605 nm, which is similar to the acid-biue form of wild-type bR. D85N shows a monophasic CD band, the maximum of which is at 575 nm, although the crystalline arrangement and the trimeric structure is rn~nt~n~. The acid-blue form of wild-type bR shows a biphasic CD despite the similarity in absorption spectra.Bacteriorhodopsin; Circular dichroism; Exciton coupling; Site-specific mutant; X-ray diffraction 1. I~RODUCTION Bacteriorhodopsin (bR), the sole protein of purple membrane of Halobacterium halobium, is a light-driven proton pump which generates a trans-membrane electroche~cal gradient [l]. bR molecules are arranged in trimers which form a two-dimensional hexagonal lattice [2,3]. The three-dimensional structure of bR at moderate resolution has been solved to clarify the locations and orientations of some amino acid residues [3]. The structural changes that occur upon formation of the M inte~ediate have been determined [4-61. The role of each amino acid residue in the proton pumping activity has been revealed by the site-directed mutagenesis (for review, see [7]). Studies using mutagenic techniques have revealed the importance of aspartates in the proton pumping activity and spectroscopic properties of bR 17-111.Replacement of D85 by N shows dramatic effects on the visible spectrum and proton-pumping activity [8,9,12]. Recently, it is shown that D85N exists as three distinct spectroscopic species in equilibrium [ 131. Turner et al. argued that these three species are closely related to M, N and 0 intermediates 1131. D85N is dominated by a blue species at pH 7, which would be related to 0, and a yellowish pigment at pH 12, which *Corresponding authors. Present address: Department of Earth and Space Science, Faculty of Science, Osaka University, Toyonaka 560, Japan. Fax: (81) (6) 845 7966. Fub~~shed by Elsevier Science publishers 3. i! 111would be related to M [13]. Structural studies of D85N is of great interest in the context of the structural analyses of the photo-intermediates.We have started intensive investigation of the structure of D85N using CD and X-ray diffraction. CD has been widely used to help understand the chromophoric properties of bR [14-171. The CD spectrum in the visible region of native bR is composed of a pair of negative and positive bands [14,15]. The origin of this biphasic shape is understood to be an exciton coupling between the chromophores in the trimeric structure of bR 116,171, although some ar~ents against the exciton model have been raised [l&19]. During the structural studies of DUN, we found that D85N shows a monophasic CD spectrum despite the fact that the crystalline structure is maintained. Here, we report the CD spectrum of D85N as compared with that of native bR. MATERIALS AND METHODS Sample preparationPurple membrane containing wild-type bR was isolated from H. haiob~~ strain RlMl by a standard procedure [20]. H. haZob...

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Section: Resultsmentioning

confidence: 99%

Trimeric mutant bacteriorhodopsin, D85N, shows a monophasic CD spectrum

et al. 1993

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“…Comparison with spectra obtained at 4 OC (below the phase transition temperature), at which extensive aggregation of BR takes place, indicates that ~7 5 % of the BR molecules in the fluid phase of the 40-rec are trimers or larger aggregates of trimers (assuming that all BR molecules are aggregated below the phase transition temperature and that the CD spectra for timers and aggregates are the same. In addition, we assume that CD spectra can be interpreted by excitons (Cassim, 1992, and references therein).…”

Section: Self-assmiationstates Of Br In Reconstituted Membranesmentioning

confidence: 99%

Molecular Organization and Dynamics in Bacteriorhodopsin-Rich Reconstituted Membranes: Discrimination of Lipid Environments by the Oxygen Transport Parameter Using a Pulse ESR Spin-Labeling Technique

Ashikawa

Yin²,

Subczynski³

et al. 1994

Biochemistry

136

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Molecular organization and dynamics in protein-rich membranes have been studied by investigating transport (diffusion-concentration product) of molecular oxygen at various locations in reconstituted membranes of bacteriorhodopsin (BR) and L-alpha-dimyristoylphosphatidylcholine. Oxygen transport was evaluated by monitoring the bimolecular collision of molecular oxygen with four types of nitroxide lipid spin labels placed at various locations in the membrane. The collision rate was estimated from the spin-lattice relaxation times (T1's) measured at various oxygen partial pressures by analyzing the short-pulse saturation recovery ESR signals. CD spectra and decay of polarized flash-induced photodichroism of bacteriorhodopsin indicated that BR molecules are monomers in reconstituted membranes with a lipid/BR molar ratio of 80 (80-rec) and are 25% monomers and 75% trimers plus oligomers of trimers when the lipid/BR ratio is 40 (40-rec). In the 80-rec, the lipid environment is homogeneous on a microsecond scale (T1), probably because the exchange rate of lipids between the bulk and the boundary regions is greater than the T1 relaxation rate (approximately 10(6) s-1). The oxygen collision rate in the hydrophobic region of the 80-rec membrane is smaller by a factor of 1.6 than in that of the lipid membrane without BR, and the effect of BR in decreasing the collision rate is independent of the "depth" in the hydrophobic region. In the 40-rec, two collision rates were observed, one of which is close to those for purple membrane (or the gel-phase membrane), while the other is about the same as was measured in the 80-rec.(ABSTRACT TRUNCATED AT 250 WORDS)

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“…No energy transfer occurs between the common carotenoid of archaea, bacterioruberin, and BR [19,20] or even archaerhodopsin which interacts with this carotenoid [2,3,21]. The much-disputed explanation for the bilobe circular dichroism (CD) spectrum of the purple membrane by an exciton interaction within the BR trimer [22], which would result in energy transfer between the three retinal molecules, disagreed with a number of experimental results [23]. However, there are several cases when energy transfer from accessory pigments to retinal is involved in photoreception.…”

Section: Introductionmentioning

confidence: 99%

Xanthorhodopsin: Proton pump with a carotenoid antenna

Balashov

Lanyi

2007

Cell. Mol. Life Sci.

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Retinal proteins function as photoreceptors and ion pumps. Xanthorhodopsin of Salinibacter ruber is a recent addition to this diverse family. Its novel and distinctive feature is a second chromophore, a carotenoid, which serves as light-harvesting antenna. Here we discuss the properties of this carotenoid/retinal complex most relevant to its function (such as the specific binding site controlled by the retinal) and its relationship to other retinal proteins (bacteriorhodopsin, archaerhodopsin, proteorhodopsin and retinal photoreceptors of archaea and eukaryotes). Antenna addition to a retinal protein has not been observed among the archaea and emerged in bacteria apparently in response to environmental conditions where light-harvesting becomes a limiting factor in retinal protein functioning.

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Unique biphasic band shape of the visible circular dichroism of bacteriorhodopsin in purple membrane

Cited by 43 publications

References 54 publications

Trimeric mutant bacteriorhodopsin, D85N, shows a monophasic CD spectrum

Trimeric mutant bacteriorhodopsin, D85N, shows a monophasic CD spectrum

Molecular Organization and Dynamics in Bacteriorhodopsin-Rich Reconstituted Membranes: Discrimination of Lipid Environments by the Oxygen Transport Parameter Using a Pulse ESR Spin-Labeling Technique

Xanthorhodopsin: Proton pump with a carotenoid antenna

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