scholarly journals Contribution of low-temperature single-molecule techniques to structural issues of pigment–protein complexes from photosynthetic purple bacteria

2018 ◽  
Vol 15 (138) ◽  
pp. 20170680 ◽  
Author(s):  
Alexander Löhner ◽  
Richard Cogdell ◽  
Jürgen Köhler
Keyword(s):  
Low Temperature ◽  
Single Molecule ◽  
Degrees Of Freedom ◽  
Protein Complexes ◽  
Purple Bacteria ◽  
Structural Models ◽  
Spectral Features ◽  
Light Harvesting Complexes ◽  
Pigment Protein Complexes ◽  
Photosynthetic Purple Bacteria

As the electronic energies of the chromophores in a pigment–protein complex are imposed by the geometrical structure of the protein, this allows the spectral information obtained to be compared with predictions derived from structural models. Thereby, the single-molecule approach is particularly suited for the elucidation of specific, distinctive spectral features that are key for a particular model structure, and that would not be observable in ensemble-averaged spectra due to the heterogeneity of the biological objects. In this concise review, we illustrate with the example of the light-harvesting complexes from photosynthetic purple bacteria how results from low-temperature single-molecule spectroscopy can be used to discriminate between different structural models. Thereby the low-temperature approach provides two advantages: (i) owing to the negligible photobleaching, very long observation times become possible, and more importantly, (ii) at cryogenic temperatures, vibrational degrees of freedom are frozen out, leading to sharper spectral features and in turn to better resolved spectra.

scholarly journals STUDY ON THE STRUCTURAL BASIS OF PERIPHERAL LIGHT HARVESTING COMPLEXES (LH2) IN PURPLE NON-SULPHUR PHOTOSYNTHETIC BACTERIA

2010 ◽  
Vol 10 (3) ◽  
pp. 401-408 ◽  
Author(s):  
Tatas H.P. Brotosudarmo ◽  
Richard J. Cogdell
Keyword(s):  
Solar Energy ◽  
Photosynthetic Bacteria ◽  
Light Harvesting ◽  
Protein Complexes ◽  
Purple Bacteria ◽  
Structural Basis ◽  
Carotenoid Pigments ◽  
Light Harvesting Complexes ◽  
Energy Funnel ◽  
Pigment Protein Complexes

Photosynthesis provides an example of a natural process that has been optimized during evolution to harness solar energy efficiently and safely, and finally to use it to produce a carbon-based fuel. Initially, solar energy is captured by the light harvesting pigment-protein complexes. In purple bacteria these antenna complexes are constructed on a rather simple modular basis. Light absorbed by these antenna complexes is funnelled downhill to reaction centres, where light drives a trans-membrane redox reaction. The light harvesting proteins not only provide the scaffolding that correctly positions the bacteriochlorophyll a and carotenoid pigments for optimal energy transfer but also creates an environment that can modulate the wavelength at which different bacteriochlorophyll molecules absorb light thereby creating the energy funnel. How these proteins can modulate the absorption spectra of the bacteriochlorophylls will be discussed in this review.

scholarly journals Fast Diffusion of the Unassembled PetC1-GFP Protein in the Cyanobacterial Thylakoid Membrane

Life ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 15
Author(s):  
Radek Kaňa ◽  
Gábor Steinbach ◽  
Roman Sobotka ◽  
György Vámosi ◽  
Josef Komenda
Keyword(s):  
Membrane Proteins ◽  
Single Molecule ◽  
Protein Interactions ◽  
Thylakoid Membrane ◽  
Protein Complexes ◽  
Correlation Spectroscopy ◽  
Membrane Microdomains ◽  
Fast Diffusion ◽  
Light Harvesting Complexes ◽  
Term Survival

Biological membranes were originally described as a fluid mosaic with uniform distribution of proteins and lipids. Later, heterogeneous membrane areas were found in many membrane systems including cyanobacterial thylakoids. In fact, cyanobacterial pigment–protein complexes (photosystems, phycobilisomes) form a heterogeneous mosaic of thylakoid membrane microdomains (MDs) restricting protein mobility. The trafficking of membrane proteins is one of the key factors for long-term survival under stress conditions, for instance during exposure to photoinhibitory light conditions. However, the mobility of unbound ‘free’ proteins in thylakoid membrane is poorly characterized. In this work, we assessed the maximal diffusional ability of a small, unbound thylakoid membrane protein by semi-single molecule FCS (fluorescence correlation spectroscopy) method in the cyanobacterium Synechocystis sp. PCC6803. We utilized a GFP-tagged variant of the cytochrome b6f subunit PetC1 (PetC1-GFP), which was not assembled in the b6f complex due to the presence of the tag. Subsequent FCS measurements have identified a very fast diffusion of the PetC1-GFP protein in the thylakoid membrane (D = 0.14 − 2.95 µm2s−1). This means that the mobility of PetC1-GFP was comparable with that of free lipids and was 50–500 times higher in comparison to the mobility of proteins (e.g., IsiA, LHCII—light-harvesting complexes of PSII) naturally associated with larger thylakoid membrane complexes like photosystems. Our results thus demonstrate the ability of free thylakoid-membrane proteins to move very fast, revealing the crucial role of protein–protein interactions in the mobility restrictions for large thylakoid protein complexes.

scholarly journals Structure of the stress-related LHCSR1 complex determined by an integrated computational strategy

2021 ◽  
Author(s):  
Ingrid Guarnetti Prandi ◽  
Vladislav Sláma ◽  
Cristina Pecorilla ◽  
Lorenzo Cupellini ◽  
Benedetta Mennucci
Keyword(s):  
Structural Model ◽  
Light Harvesting ◽  
Structural Information ◽  
Protein Complexes ◽  
Complex Stress ◽  
Main Function ◽  
Light Harvesting Complexes ◽  
Light Harvesting Complex ◽  
Pigment Protein Complexes ◽  
Computational Strategy

Light-harvesting complexes (LHCs) are pigment-protein complexes whose main function is to capture sunlight and transfer the energy to reaction centers of photosystems. In response to varying light conditions, LH complexes also play photoregulation and photoprotection roles. In algae and mosses, a sub-family of LHCs, Light-Harvesting complex stress related (LHCSR), is responsible for photoprotective quenching. Despite their functional and evolutionary importance, no direct structural information on LHCSRs is available that can explain their unique properties. In this work we propose a structural model of LHCSR1 from the moss P. Patens, obtained through an integrated computational strategy that combines homology modeling, molecular dynamics, and multiscale quantum chemical calculations. The model is validated by reproducing the spectral properties of LHCSR1. Our model reveals the structural specificity of LHCSR1, as compared with the CP29 LH complex, and poses the basis for understanding photoprotective quenching in mosses.

Two-photon excitation spectroscopy of photosynthetic light-harvesting complexes and pigments

2019 ◽  
Vol 216 ◽  
pp. 494-506 ◽  
Author(s):  
Alexander Betke ◽  
Heiko Lokstein
Keyword(s):  
Spectral Region ◽  
Protein Complexes ◽  
Photosynthetic Pigment ◽  
Photon Absorption ◽  
Light Harvesting Complexes ◽  
Two Photon Absorption ◽  
Two Photon ◽  
Photon Excitation ◽  
Pigment Protein Complexes ◽  
Two Photon Excitation

Two-photon excitation (TPE) profiles of LHCII samples containing different xanthophyll complements were measured in the presumed 11Ag− → 21Ag− (S0 → S1) transition region of xanthophylls. Additionally, TPE profiles of Chls a and b in solution and of WSCP, which does not contain carotenoids, were measured. The results indicate that direct two-photon absorption by Chls in the presumed S0 → S1 transition spectral region of carotenoids is dominant over that of carotenoids, with negligible contributions of the latter. These results suggest the re-evaluation of previously published TPE data obtained with photosynthetic pigment–protein complexes containing (B)Chls and carotenoids.

scholarly journals A photosynthetic antenna complex foregoes unity carotenoid-to-bacteriochlorophyll energy transfer efficiency to ensure photoprotection

2020 ◽  
Vol 117 (12) ◽  
pp. 6502-6508 ◽  
Author(s):  
Dariusz M. Niedzwiedzki ◽  
David J. K. Swainsbury ◽  
Daniel P. Canniffe ◽  
C. Neil Hunter ◽  
Andrew Hitchcock
Keyword(s):  
Energy Transfer ◽  
Transient Absorption ◽  
Light Harvesting ◽  
Protein Complexes ◽  
Fluorescence Emission ◽  
Energy Transfer Efficiency ◽  
Transfer Efficiency ◽  
Light Harvesting Complexes ◽  
Antenna Complex ◽  
Pigment Protein Complexes

Carotenoids play a number of important roles in photosynthesis, primarily providing light-harvesting and photoprotective energy dissipation functions within pigment–protein complexes. The carbon–carbon double bond (C=C) conjugation length of carotenoids (N), generally between 9 and 15, determines the carotenoid-to-(bacterio)chlorophyll [(B)Chl] energy transfer efficiency. Here we purified and spectroscopically characterized light-harvesting complex 2 (LH2) fromRhodobacter sphaeroidescontaining theN= 7 carotenoid zeta (ζ)-carotene, not previously incorporated within a natural antenna complex. Transient absorption and time-resolved fluorescence show that, relative to the lifetime of the S1state of ζ-carotene in solvent, the lifetime decreases ∼250-fold when ζ-carotene is incorporated within LH2, due to transfer of excitation energy to the B800 and B850 BChlsa. These measurements show that energy transfer proceeds with an efficiency of ∼100%, primarily via the S1→ Qxroute because the S1→ S0fluorescence emission of ζ-carotene overlaps almost perfectly with the Qxabsorption band of the BChls. However, transient absorption measurements performed on microsecond timescales reveal that, unlike the nativeN≥ 9 carotenoids normally utilized in light-harvesting complexes, ζ-carotene does not quench excited triplet states of BChla, likely due to elevation of the ζ-carotene triplet energy state above that of BChla. These findings provide insights into the coevolution of photosynthetic pigments and pigment–protein complexes. We propose that theN≥ 9 carotenoids found in light-harvesting antenna complexes represent a vital compromise that retains an acceptable level of energy transfer from carotenoids to (B)Chls while allowing acquisition of a new, essential function, namely, photoprotective quenching of harmful (B)Chl triplets.

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