High pressure near infrared study of the mutated light-harvesting complex LH2

Braun, Paula; Gebhardt, Ronald; Kwa, Lee Gyan; Doster, Wolfgang

doi:10.1590/s0100-879x2005000800017

Cited by 7 publications

(5 citation statements)

References 17 publications

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“…4). Most of the interactions between α-polypeptide and β-polypeptide in LH2 occur close to the membranewater interfaces, between the C and N termini lying on the membrane, while the pigments (both BChl and carotenoid molecules) mediate most of the contacts between α and β in the hydrophobic phase (33,34). The AFM unfolding experiments were performed on LH2 complexes viewed from the periplasmic photosynthetic membrane surface (see Fig.…”

Section: Resultsmentioning

confidence: 99%

Forces guiding assembly of light-harvesting complex 2 in native membranes

Liu

Duquesne

Oesterhelt

et al. 2011

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

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Interaction forces of membrane protein subunits are of importance in their structure, assembly, membrane insertion, and function. In biological membranes, and in the photosynthetic apparatus as a paradigm, membrane proteins fulfill their function by ensemble actions integrating a tight assembly of several proteins. In the bacterial photosynthetic apparatus light-harvesting complexes 2 (LH2) transfer light energy to neighboring tightly associated core complexes, constituted of light-harvesting complexes 1 (LH1) and reaction centers (RC). While the architecture of the photosynthetic unit has been described, the forces and energies assuring the structural and functional integrity of LH2, the assembly of LH2 complexes, and how LH2 interact with the other proteins in the supramolecular architecture are still unknown. Here we investigate the molecular forces of the bacterial LH2 within the native photosynthetic membrane using atomic force microscopy single-molecule imaging and force measurement in combination. The binding between LH2 subunits is fairly weak, of the order of k B T , indicating the importance of LH2 ring architecture. In contrast LH2 subunits are solid with a free energy difference of 90 k B T between folded and unfolded states. Subunit α-helices unfold either in one-step, α-and β-polypeptides unfold together, or sequentially. The unfolding force of transmembrane helices is approximately 150 pN. In the two-step unfolding process, the β-polypeptide is stabilized by the molecular environment in the membrane. Hence, intermolecular forces influence the structural and functional integrity of LH2.atomic force microscopy | photosynthesis | protein unfolding | membrane protein assembly M embrane protein function is intimately linked and influenced by its structural integrity and molecular environment (1-3). Photosynthesis is a paradigm of such orchestrated molecular action, for which the implicated proteins have evolved to form supramolecular assemblies (4). Knowledge of supramolecular architecture and interaction forces and energies are indispensable for a complete understanding of a membrane protein structure and function.The atomic force microscope (AFM) (5) can be used as a high-resolution imaging (6) and as a force-measurement tool (7). Most elegantly the two applications were combined allowing the attribution of structural changes to force events (8). More recently, the AFM has proven the unique tool for studying the supramolecular assembly of the bacterial photosynthetic unit (9-12) and has provided a solid basis for the understanding of the ensemble function of the photosynthetic proteins (4, 13-15).The light-harvesting process in photosynthetic bacteria starts with photon capture at the peripheral light-harvesting complex 2 (LH2) that transfers the absorbed excitation energy to the light-harvesting complex 1 (LH1) associated with the reaction center (RC). The LH2 structure is well described by X-ray crystallography (16, 17) and AFM in native membranes (12,(18)(19)(20). Typically, the LH2 complexes appe...

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Section: Resultsmentioning

confidence: 99%

Forces guiding assembly of light-harvesting complex 2 in native membranes

Liu

Duquesne

Oesterhelt

et al. 2011

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

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“…The effect of changing the strength of the interactions between the Bchla molecules in the B850 ring can be probed by recording the absorption spectrum either as a function of temperature or pressure (Tars et al 1994 ;Reddy et al 1996 ;Wu et al 1996Wu et al , 1997aTimpmann et al 2001 ;Matsuzaki et al 2001 ;Zazubovich et al 2002b ;Gall et al 2003b ;Braun et al 2005 ;Urboniene et al 2005). As the temperature is lowered from room temperature to y150 K the position of the 850 nm absorption band in LH2 from Rps.…”

Section: Factors Which Affect the Position Of The Q Y Absorption Bandmentioning

confidence: 99%

The architecture and function of the light-harvesting apparatus of purple bacteria: from single molecules to in vivo membranes

Cogdell

Gall

Köhler

2006

Quart. Rev. Biophys.

636

734

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This review describes the structures of the two major integral membrane pigment complexes, the RC-LH1 'core' and LH2 complexes, which together make up the light-harvesting system present in typical purple photosynthetic bacteria. The antenna complexes serve to absorb incident solar radiation and to transfer it to the reaction centres, where it is used to 'power' the photosynthetic redox reaction and ultimately leads to the synthesis of ATP. Our current understanding of the biosynthesis and assembly of the LH and RC complexes is described, with special emphasis on the roles of the newly described bacteriophytochromes. Using both the structural information and that obtained from a wide variety of biophysical techniques, the details of each of the different energy-transfer reactions that occur, between the absorption of a photon and the charge separation in the RC, are described. Special emphasis is given to show how the use of single-molecule spectroscopy has provided a more detailed understanding of the molecular mechanisms involved in the energy-transfer processes. We have tried, with the help of an Appendix, to make the details of the quantum mechanics that are required to appreciate these molecular mechanisms, accessible to mathematically illiterate biologists. The elegance of the purple bacterial light-harvesting system lies in the way in which it has cleverly exploited quantum mechanics.

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“…The experiments firmly established that distortions induced by high hydrostatic pressures involve the whole bulk of the antenna proteins, not only the binding sites of the 800 nm-absorbing Bchl molecules demonstrated earlier. [8][9][10][11][12][13][14][15][16][17] Hydrogen bond brakeage in the B850 pigment system occurs at pressures above 0.5 GPa, depending on relative concentration of the protein and LDAO. Preliminary results of this work have been reported.…”

Section: Introductionmentioning

confidence: 99%

“…The photosynthetic membrane pigment−protein complexes, especially the bacterial light-harvesting complexes, frequently demonstrate clear-cut structure related to different spatial arrangements of the pigments. Due to this advantage, a number of bacterial antenna complexes have been tried under high pressure. – These early works have shown that hydrostatic pressure almost universally leads to a monotonous low-energy shift (red-shift for short) and broadening of the antenna absorption bands. For the peripheral antenna complex from purple photosynthetic bacteria called light-harvesting complex 2 (LH2), which is one of the best-characterized integral membrane proteins, a loss of the 800 nm-absorbing bacteriochlorophyll a (Bchl) molecules in purified LH2 complexes from Rhodobacter (Rb.)…”

Section: Introductionmentioning

confidence: 99%

Stability of Integral Membrane Proteins under High Hydrostatic Pressure: The LH2 and LH3 Antenna Pigment−Protein Complexes from Photosynthetic Bacteria

2008

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The bacteriochlorophyll a-containing LH2 and LH3 antenna complexes are the integral membrane proteins that catalyze the photosynthetic process in purple photosynthetic bacteria. The LH2 complex from Rhodobacter sphaeroides shows characteristic strong absorbance at 800 and 850 nm due to the pigment molecules confined in two separate areas of the protein. In the LH3 complex from Rhodopesudomonas acidophila the corresponding bands peak at 800 and 820 nm. Using the bacteriochlorophyll a cofactors as intrinsic probes to monitor local changes in the protein structure, we investigate spectral responses of the antenna complexes to very high hydrostatic pressures up to 2.5 GPa when embedded into natural membrane environment or extracted with detergent. We first demonstrate that high pressure does induce significant alterations to the tertiary structure of the proteins not only in proximity of the 800 nm-absorbing bacteriochlorophyll a molecules known previously (Gall, A.; et al. Biochemistry 2003, 42, 13019) but also of the 850 nm- and 820 nm-absorbing molecules, including breakage of the hydrogen bond they are involved in. The membrane-protected complexes appear more resilient to damaging effects of the compression compared with the complexes extracted into mixed detergent-buffer environment. Increased resistance of the isolated complexes is observed at high protein concentration resulting aggregation as well as when cosolvent (glycerol) is added into the solution. These stability variations correlate with ability of penetration of the surrounding polar solvent (water) into the hydrophobic protein interiors, being thus the principal reason of the pressure-induced denaturation of the proteins. Considerable variability of elastic properties of the isolated complexes was also observed, tentatively assigned to heterogeneous protein packing in detergent micelles. While a number of the isolated complexes release most of their bacteriochlorophyll a content under high pressure, quite some of them remain apparently intact. The pigmented photosynthetic antenna complexes thus constitute a suitable model system for studying in detail the stability of integral membrane proteins.

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High pressure near infrared study of the mutated light-harvesting complex LH2

Cited by 7 publications

References 17 publications

Forces guiding assembly of light-harvesting complex 2 in native membranes

Forces guiding assembly of light-harvesting complex 2 in native membranes

The architecture and function of the light-harvesting apparatus of purple bacteria: from single molecules to in vivo membranes

Stability of Integral Membrane Proteins under High Hydrostatic Pressure: The LH2 and LH3 Antenna Pigment−Protein Complexes from Photosynthetic Bacteria

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