Spectroscopy and structure of bacteriochlorophyll dimers. I. Structural consequences of nonconservative circular dichroism spectra

Koolhaas, M.H.C.; Zwan, Gert van der; Mourik, Frank van; Grondelle, Rienk van

doi:10.1016/s0006-3495(97)78829-5

Cited by 36 publications

(40 citation statements)

References 22 publications

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“…It is, therefore, possible to ascribe the nonconservativity of the NIR CD signals from carotenoid-less LH1 mutants (i.e., as in a recent study by Lupo and Gosh 63 ) to interactions with higher BChl transitions. 64 However, it is not possible to produce completely negative signals based solely on the interaction of the BChl Q Y transitions with the Soret. The need to take more interactions into account, the ones in the visible part of the spectrum, is clearly evident.…”

Section: Resultsmentioning

confidence: 99%

Investigation of the Effects of Different Carotenoids on the Absorption and CD Signals of Light Harvesting 1 Complexes

et al. 2006

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Absorption and circular dichroism (CD) spectra of light-harvesting (LH)1 complexes from the purple bacteria Rhodobacter (Rba.) sphaeroides and Rhodospirillum (Rsp.) rubrum are presented. The complexes exhibit very low intensity, highly nonconservative, near-infrared (NIR) CD spectra. Absorption and CD spectra from several mutant and reconstituted LH1 complexes, with the carotenoid neurosporene and the precursor phytoene replacing the wild-type (WT) carotenoids, are also examined. The experiments show that the position of the carotenoid bands as well as the bacteriochlorophyll (BChl)/carotenoid ratio affect the NIR CD spectra: bluer bands and larger ratios make the NIR CD signal more conservative. Modeling results that support this finding are presented. This study, combined with the theoretical approach of the companion paper, where modeling of such complexes is presented and discussed in detail, provide a complete explanation of the origin of the nonconservative NIR CD spectra of LH1 and B820.

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Section: Resultsmentioning

confidence: 99%

Investigation of the Effects of Different Carotenoids on the Absorption and CD Signals of Light Harvesting 1 Complexes

et al. 2006

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“…The model (which is the same as used in ref. 21) is built on the same theoretical grounds as the one used successfully to model excitonic couplings in photosynthetic reaction centers (41). Tryptophan residues are described by a ground state and 2 almost degenerate excited electronic states, namely L b and La.…”

Section: Methodsmentioning

confidence: 99%

Functional electric field changes in photoactivated proteins revealed by ultrafast Stark spectroscopy of the Trp residues

Léonard

Portuondo-Campa

Cannizzo

et al. 2009

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

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retinal proteins ͉ dipolar interactions ͉ tryptophan ͉ ultraviolet probe T he membrane protein bacteriorhodopsin (bR) is a proton pump, the biological activity of which is triggered by the absorption of light by the protonated retinal cofactor (1, 2). On light excitation, the retinal moiety undergoes an isomerization from 13-cis to all-trans that proceeds with very high speed (Ϸ0.5 ps) and large quantum efficiency (Ϸ0.64). In the excited Franck-Condon state, before isomerization, a large photoinduced charge translocation along retinal increases its dipole moment by as much as 10-30 D (3, 4). Remarkably, the photoisomerization of the same chromophore in any environment other than that of the natural protein scaffold is no longer specific and it is less efficient and slower (5), indicating the enzymatic role of the protein environment that enhances the speed and selectivity of the retinal isomerization. Site-directed mutagenesis has shown that charged amino acid residues closely interacting with the charged retinal moiety (Arg 82 , Asp 85 , Asp 212 ) largely influence the isomerization speed (6, 7). Theoretical investigations of a retinal-like model compound (8) rationalize these findings in modeling how a chloride counterion affects the energetics and photoreactivity. In addition, within the protein, the large photoinduced charge translocation along retinal is expected to induce a strong, ultrafast dielectric response of the full protein environment (9, 10), which could also participate in the enzymatic function by driving specifically the isomerization path to all-trans retinal. Besides, the exact nature of the driving force for the biological activity of the protein has long been (11) and still is a subject of intensive investigations. Hence, protein conformational changes similar to those observed in functional wild-type (WT) bR have been observed in artificial proteins with nonisomerizing retinal chromophores (12), suggesting that the initial charge translocation alone would activate the modified proteins. In the initial steps of the photocycle, the protein has to convert and store light energy, so as to drive the primary proton transfer from the protonated retinal to the Asp 85 counter ion, and successive proton transfer reactions via small conformational rearrangements of the protein. Several origins have been proposed and debated for the dominating driving force leading to the primary and subsequent proton transfers, among which are (i) energy storage in the strained geometry of the isomerized chromophore (13), and (ii) electrostatic energy storage (14), either mainly due to the modification by the isomerization of the electrostatic interactions between the protein and the donor/ acceptor pair (15), or to a light-induced charge separation between primary proton donor and acceptor (16).To investigate the light-induced electrostatic and/or dielectric modifications along or in the vicinity of retinal, we performed ultrafast absorption spectroscopy on the nearby tryptophan residues. Wild-type bR contains 8 try...

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“…It is well known that disubstitution of an organic compound with strongly interacting chromophores can lead to coupling of the electronic states and splitting of the energy levels (12)(13)(14). The arrangement of transition dipoles affects both the splitting and the transition intensities, which can be detected spectroscopically.…”

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confidence: 99%

Conformation of self-assembled porphyrin dimers in liposome vesicles by phase-modulation 2D fluorescence spectroscopy

Lott

Perdomo-Ortiz

Utterback

et al. 2011

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

112

160

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By applying a phase-modulation fluorescence approach to 2D electronic spectroscopy, we studied the conformation-dependent exciton coupling of a porphyrin dimer embedded in a phospholipid bilayer membrane. Our measurements specify the relative angle and separation between interacting electronic transition dipole moments and thus provide a detailed characterization of dimer conformation. Phase-modulation 2D fluorescence spectroscopy (PM-2D FS) produces 2D spectra with distinct optical features, similar to those obtained using 2D photon-echo spectroscopy. Specifically, we studied magnesium meso tetraphenylporphyrin dimers, which form in the amphiphilic regions of 1,2-distearoyl-sn-glycero-3-phosphocholine liposomes. Comparison between experimental and simulated spectra show that although a wide range of dimer conformations can be inferred by either the linear absorption spectrum or the 2D spectrum alone, consideration of both types of spectra constrain the possible structures to a "T-shaped" geometry. These experiments establish the PM-2D FS method as an effective approach to elucidate chromophore dimer conformation.fluorescence-detected 2D photon echo | nonlinear spectroscopy | supramolecular conformation | excitonically coupled dimer T he ability to determine three-dimensional structures of macromolecules and macromolecular complexes plays a central role in the fields of molecular biology and material science. Methods to extract structural information from experimental observations such as X-ray crystallography, NMR, and optical spectroscopy are routinely applied to a diverse array of problems, ranging from investigations of biological structure-function relationships to the chemical basis of molecular recognition.In recent years, two-dimensional optical methods have become well established to reveal incisive information about noncrystalline macromolecular systems-information that is not readily obtainable by conventional linear spectroscopic techniques. Twodimensional optical spectroscopy probes the nanometer-scale couplings between vibrational or electronic transition dipole moments of neighboring chemical groups, similar to the way NMR detects the angstrom-scale couplings between adjacent nuclear spins in molecules (1). For example, 2D IR spectroscopy probes the couplings between local molecular vibrational modes and has been used to study the structure and dynamics of mixtures of molecular liquids (2), aqueous solutions of proteins (3), and DNA (4). Similarly, 2D electronic spectroscopy (2D ES) probes correlations of electronic transitions and has been used to study the mechanisms of energy transfer in multichromophore complexes. Such experiments have investigated the details of femtosecond energy transfer in photosynthetic protein-pigment arrays (5-8), conjugated polymers (9), and semiconductors (10, 11).Following the examples established by 2D NMR and 2D IR, 2D ES holds promise as a general approach for the structural analysis of noncrystalline macromolecular systems, albeit for the nanometer length scales ...

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Spectroscopy and structure of bacteriochlorophyll dimers. I. Structural consequences of nonconservative circular dichroism spectra

Cited by 36 publications

References 22 publications

Investigation of the Effects of Different Carotenoids on the Absorption and CD Signals of Light Harvesting 1 Complexes

Investigation of the Effects of Different Carotenoids on the Absorption and CD Signals of Light Harvesting 1 Complexes

Functional electric field changes in photoactivated proteins revealed by ultrafast Stark spectroscopy of the Trp residues

Conformation of self-assembled porphyrin dimers in liposome vesicles by phase-modulation 2D fluorescence spectroscopy

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