Circular dichroism of heterochromophoric and partially regenerated purple membrane: Search for exciton coupling

Karnaukhova, Elena; Vasileiou, Chrysoula; Wang, Andy; Nina, Berova; Nakanishi, Koji; Borhan, Babak

doi:10.1002/chir.20222

Cited by 12 publications

(27 citation statements)

References 71 publications

(46 reference statements)

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“…2d, 3d and 4d). In a previously reported AFM study, bO produced following the bleaching of WT‐bR were unable to form hexagonal lattices despite the retention of the trimeric unit (11). It is suggested that the lack of the correct BC loop structure in bO leads to the disorganized lattice formation (Figs.…”

Section: Resultsmentioning

confidence: 98%

“…The results from atomic force microscopy (AFM) experiments have indicated that the trimeric form of bR is preserved in the PM, although the lattice disappeared following PM bleaching (8). In addition, the trimeric organization of partially and fully regenerated bR has been revealed by CD spectra (11), and the high yield of regenerated bR has been reported to be produced from thermally unfolded bO (12). These characteristics of retinal-reconstituted bR appear to be different to that of WT-bR.…”

Section: Introductionmentioning

confidence: 99%

“…These thermal properties of the BC loop may also be associated with its function in addition to the structural stability of bR. In particular, NMR chemical shifts of [1,[2][3][4][5][6][7][8][9][10][11][12][13] C]Val69, [ 15 N]Pro70 and [1-13 C]Ile78 in bR indicated the formation of a b-sheet structure when the conformationdependent chemical shifts were investigated (16,17). We have recently revealed that the dynamic structure of the BC loop in WT-bR contains a rigid b-sheet conformation with a largeamplitude motion using solid-state NMR techniques (16).…”

Section: Introductionmentioning

confidence: 99%

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Participation of the BC Loop in the Correct Folding of Bacteriorhodopsin as Revealed by Solid-state NMR

Kawamura

Tanabe

Ohmine

et al. 2009

Photochemistry and Photobiology

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Structural changes in bacteriorhodopsin (bR) in two different processes of retinal reconstitutions were investigated by observing the (13)C and (15)N solid-state NMR spectra of [1-(13)C]Val- and [(15)N]Pro-labeled bR. We found that NMR signals of the BC loop were sensitive to changes in protein structure and dynamics, from wild-type (WT) bR to bacterio-opsin (bO), regenerated bR and E1001 bR. Regenerated bR was prepared following the addition of retinal into bO obtained from photobleached WT-bR. E1001 bR was cultured from a retinal-deficient strain termed E1001 following the addition of retinal to growing cells. (15)N NMR signal at Pro70 in the BC loop in WT-bR was observed at 122.4 p.p.m., whereas signals were not apparent or partly suppressed in bO and regenerated bR, respectively. Similarly, the (13)C NMR signal at Val69 in the BC loop at 172.0 p.p.m. that was observed in WT-bR was significantly decreased in both regenerated bR and bO. These results suggest that the dynamic structure of the BC loop in bO was substantially altered following the removal of retinal. As a consequence, the correct protein structure failed to be recovered via the regenerating process of retinal to bO. On the other hand, (13)C and (15)N NMR signals at the BC loop in E1001 bR appeared at positions identical to those of WT-bR. The results of the current study indicate that the BC loop may not always fold correctly in the regenerated bR, which leads to different properties in the regenerated bR compared to that of WT-bR.

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Section: Resultsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Participation of the BC Loop in the Correct Folding of Bacteriorhodopsin as Revealed by Solid-state NMR

Kawamura

Tanabe

Ohmine

et al. 2009

Photochemistry and Photobiology

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“…The first possibility is based on excitonic interaction between sal and the retinal chromophore 21 . The second stems from the chiral conformation of the retinal in the presence of sal, while retinal-retinal excitonic coupling in a pigment pentamer form can be an additional cause for the CD spectrum 15,24,26,27 . Another possibility is based on a chiral conformation of sal in the presence of the retinal chromophore and nearby protein residues 19 .…”

Section: Discussionmentioning

confidence: 99%

“…Although the CD spectra of native bR, and xR-sal complex were widely studied, the exact origin of the CD spectra is not completely clear 18,19,21,23,24,[27][28][29][30][31][32] . The CD spectra of native gR as well as in the presence of different types of carotenoids were studied previously, and it was proposed that the CD of the gR-carotenoid complex is due to induced chirality of the carotenoid 10,11 .…”

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confidence: 99%

The chirality origin of retinal-carotenoid complex in gloeobacter rhodopsin: a temperature-dependent excitonic coupling

Jana

Jung

Sheves

2020

Sci Rep

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Retinal proteins play significant roles in light-induced protons/ions transport across the cell membrane. A recent studied retinal protein, gloeobacter rhodopsin (gR), functions as a proton pump, and binds the carotenoid salinixanthin (sal) in addition to the retinal chromophore. We have studied the interactions between the two chromophores as reflected in the circular dichroism (CD) spectrum of gR complex. gR exhibits a weak CD spectrum but following binding of sal, it exhibits a significant enhancement of the CD bands. To examine the CD origin, we have substituted the retinal chromophore of gR by synthetic retinal analogues, and have concluded that the CD bands originated from excitonic interaction between sal and the retinal chromophore as well as the sal chirality induced by binding to the protein. Temperature increase significantly affected the CD spectra, due to vanishing of excitonic coupling. A similar phenomenon of excitonic interaction lose between chromophores was recently reported for a photosynthetic pigment-protein complex (Nature Commmun, 9, 2018, 99). We propose that the excitonic interaction in gR is weaker due to protein conformational alterations. The excitonic interaction is further diminished following reduction of the retinal protonated Schiff base double bond. Furthermore, the intact structure of the retinal ring is necessary for obtaining the excitonic interaction. Abbreviations gR Gloeobacter rhodopsin Apo-gR/apo Apo-protein of gR Sal Salinixanthin CD Circular Dichroism xR Xanthorhodopsin bR Bacteriorhodopsin wt-bR Wild type bacteriorhodopsin DDM N-Dodecyl β-d-maltoside SDS Sodium dodecyl sulphate EC Excitonic coupling CE Cotton effect NaBH 4 Sodium borohydride PBS Protonated Schiff base Gloeobacter rhodopsin (gR) is a recently studied retinal protein which was found in thylakoid-less unicellular cyanobacterium Gloeobacter violaceus Pcc 7421 1,2 , heterogeneously expressed in E. coli.

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ECD exciton chirality method today: a modern tool for determining absolute configurations

Pescitelli

2021

Chirality

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The application of the exciton chirality method (ECM) to interpret electronic circular dichroism (ECD) spectra is a well-established and still popular approach to assign the absolute configuration (AC) of natural products, chiral organic compounds, and organometallic species. The method applies to compounds containing at least two chromophores with electric dipole allowed transitions (e.g., π-π* transitions). The exciton chirality rule correlates the sign of an exciton couplet (two ECD bands with opposite sign and similar intensity) with the overall molecular stereochemistry, including the AC. A correct application of the ECM requires three main prerequisites: (a) the knowledge of the molecular conformation, (b) the knowledge of the directions of the electric transition moments (TDMs), and (c) the assumption that the exciton coupling mechanism must be the major source of the observed ECD signals. All these prerequisites can be easily verified by means of quantum-mechanical (QM) calculations. In the present review, we shortly introduce the general principles that underpin the use of the ECM for configurational assignments and survey its applications, both classic ones and some reported in the recent literature. Based on these examples, we will stress the advantages of the ECM but also the key requisites for its correct application. Additionally, we will discuss the dependence of the couplet sign on geometrical parameters (angles α,β,γ between TDMs), which can be helpful for discerning the sign of exciton chirality in ambiguous situations. Finally, we will present a molecular orbital (MO) description of the exciton coupling phenomenon.

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Circular dichroism of heterochromophoric and partially regenerated purple membrane: Search for exciton coupling

Cited by 12 publications

References 71 publications

Participation of the BC Loop in the Correct Folding of Bacteriorhodopsin as Revealed by Solid-state NMR

Participation of the BC Loop in the Correct Folding of Bacteriorhodopsin as Revealed by Solid-state NMR

The chirality origin of retinal-carotenoid complex in gloeobacter rhodopsin: a temperature-dependent excitonic coupling

ECD exciton chirality method today: a modern tool for determining absolute configurations

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