Design and Assembly of Functional Light-Harvesting Complexes

Braun, Paula; Fiedor, Leszek

doi:10.1007/978-1-4020-8815-5_46

Cited by 7 publications

(5 citation statements)

References 121 publications

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“…The choice of cosolvent was made after testing a series of solvents, screened for being optimal Crt carriers in our LH1 reconstitution approach. ,,, Among the many solvents tested (ethanol, acetone, diethyl ether, methanol, 2-propanol, tetrahydrofuran, ACN, benzene, and n -hexane), acetone gave the best results. The choice of detergent (LDAO) and its concentration, 0.033%, slightly above the cmc value, was also found critical for LH1 formation and Crt insertion.…”

Section: Discussionmentioning

confidence: 99%

“…This points to the dominant role of π−π interactions in the binding of Crts to LH1. Indeed, recent theoretical calculations, mutagenesis, and statistical analyses of Crt binding sites have shown the key importance of π−π interactions between Crts and the aromatic residues of LH2 apoproteins, ,− and peridinins and the aromatic residues of the peridinin−chlorophyll−protein complex of Amphidinium carterae. Such interactions have also been shown to play an essential role in binding β-carotenes to aromatic residues in photosystem I .…”

Section: Discussionmentioning

confidence: 99%

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Tuning the Thermodynamics of Association of Transmembrane Helices

2009

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Modular photosynthetic LH1 complex is applied as a model system to investigate the thermodynamics of a self-assembling membrane protein and the effects of cosolvents and cofactor (carotenoid) on the process. Native chromophores of LH1, bacteriochlorophyll, and carotenoid are excellent intrinsic spectroscopic reporter molecules. Their presence allows us to follow the association of transmembrane helices of LH1, without the use of any external markers, by electronic absorption/emission and circular dichroism. Furthermore, the assembly correctness can be monitored by the intracomplex energy transfer. Both the cosolvent and carotenoid markedly affect DeltaH degrees and DeltaS degrees associated with the complex formation in detergent, but the driving force of the process remains almost constant due to an efficient enthalpy-entropy compensation in the system. In the absence of cosolvent and cofactor, the energy of interactions between transmembrane helices in LH1 equals -580 kJ/mol. DeltaH degrees drastically increases upon the addition of acetone (-1160 kJ/mol) and carotenoid (-1900 kJ/mol), whereas DeltaS degrees lowers from +1.5 kJ/mol.K to -0.4 kJ/mol.K and to -2.6 kJ/mol.K, respectively. The stabilization of the ensemble by cofactor seems to be due to the pi-pi stacking of aromatic residues of LH1 polypeptides with the carotenoid pi-electron system. The cosolvent, lowering the medium permittivity and thus enhancing helix-helix interactions, has an ordering effect on the system (DeltaS degrees<0). This effect of cosolvent on DeltaH degrees and DeltaS degrees of association of transmembrane helices is relevant for crystallization of membrane proteins, as it explains in thermodynamic terms the action of amphiphiles used for crystallization of membrane proteins in the micellar phase.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Tuning the Thermodynamics of Association of Transmembrane Helices

2009

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“…Braun et al 2011;Braun and Fiedor, 2009;Dezi et al 2007;Fowler et al 1994). The excitonically coupled BChl of purple bacterial LH1 complexes usually have their red-most transition at around 870-890 nm.…”

Section: Introductionmentioning

confidence: 99%

Ca2+-binding reduces conformational flexibility of RC–LH1 core complex from thermophile Thermochromatium tepidum

2012

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The light-harvesting complex, LH1, of thermophile purple bacteria Thermochromatium tepidum consists of an array of α- and β-polypeptides which assemble the photoactive bacteriochlorophyll and closely interact with the membrane-lipids. In this study, we investigated the effect of calcium and manganese ions on the protein structure and thermostability of the reaction centre (RC)-LH1/lipid complex. The binding of Ca(2+), but not Mn(2+) is shown to shift the LH1 Q ( y ) absorption maximum from ~889 to 915 nm and to significantly raise the thermostability of the RC-LH1 complex. The ATR-FTIR spectra indicate that interaction of Ca(2+) as monitored by the carboxylates' vibration of aspartate residues, but not Mn(2+) induces changes in the α-helix packing arrangement. The reduced rate of (1)H/(2)H exchange of proteins' amide protons shows that the accessibility to (2)H(2)O is significantly lowered in Ca(2+)-substituted RC-LH1/lipid complexes. In particular, exchange with the associated lipid molecules, is significantly retarded. These results suggest that the thermostability of the RC-LH1 complex is raised by the distinct interaction with calcium cations which reduces the RC-LH1/lipid dynamics, particularly, at the membrane-water interface.

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“…The LH1 antenna, being an assembly of relatively simple identical subunits, is perhaps the simplest type of photosynthetic antenna complex and the reversibility of its association-dissociation in micellar media renders it a very attractive model complex [2,17,18]. In the present paper, the techniques which enable for construction of model LH1 complexes from chemically modied components are described and discussed.…”

Section: Introductionmentioning

confidence: 99%

Controlling Structural and Functional Features of Photosynthetic Antenna

Fiedor

Pilch

et al. 2012

Acta Phys. Pol. A

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In order to gain control over the assembly and functioning of photosynthetic antenna, we have developed methods to manipulate pigment composition of bacterial LH1 complexes via their reconstitution with modied bacteriochlorophylls or carotenoids, major photoactive cofactors of these antennae. In the present work we show how the reconstitution and pigment exchange approach is applied to control structural and functional parameters of LH1 and its subunits. The size of the subunits and the energy of the rst excited singlet state can be controlled via the use of detergent while the thermodynamics of LH1 formation can be modied using carotenoids and/or a co-solvent. Carotenoids aect the eciency of the intracomplex energy transfer, while the replacement of native bacteriochlorophyll a with its Ni-substituted analog allows one to control the excited state properties of LH1. These results show that LH1 is a very promising model system applicable for the design of bio-inspired device performing solar energy conversion.

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Design and Assembly of Functional Light-Harvesting Complexes

Cited by 7 publications

References 121 publications

Tuning the Thermodynamics of Association of Transmembrane Helices

Tuning the Thermodynamics of Association of Transmembrane Helices

Ca2+-binding reduces conformational flexibility of RC–LH1 core complex from thermophile Thermochromatium tepidum

Controlling Structural and Functional Features of Photosynthetic Antenna

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