Energy Converting Biological Membranes
Project details
Finding efficient and environmentally friendly energy resources for supporting the rapidly increasing energy consumption of humanity became one of the primary goals of present scientific research. Understanding through fundamental research the biological systems which serve as the energy input for the current terrestrial life can take us one step closer to this goal.
In the biosphere phototroph organisms developed various strategies for efficient capture and transformation of the solar energy into chemical energy. Higher plants, cyanobacteria and various algal cells developed thylakoid membrane – the most abundant membrane on earth – which has a crucial role in the primary steps of photosynthesis. This membrane separates two aqueous phase (the stroma and the lumen) and incorporates virtually all protein complexes involved in the light reactions of photosynthesis. The macroorganization of the thylakoids, which show significant variations among the different organisms, has a high flexibility and can be easily influenced by variations in the environmental parameters. This structural flexibility has a crucial role in the adaptation capabilities of the photosynthetic aparatii to the changing environment. Small angle neutron scattering, as a non invasive experimental method, which can also capitalize on the possibility of contrast variation, is an ideal tool for the study of these reorganizations. Our experiments allowed determination of characteristic repeat distances of thylakoid membranes isolated from plants, in cyanobacteria and in diatom, revealed their light-induced reversible reorganizations and helped to understand some of the driving forces for these mechanisms [1]. In diatoms we could connect the observed changes in the lamellar order of the membranes with changes in the long-range chiral order (measured by circular dichroism) of the incorporated chromophores [2]. We also followed the influence of external parameters as osmolarity, ionic strength or strong illumination on the periodicity of thylakoid membranes of higher plants [3]. SANS allowed to follow the kinetics of the membrane reorganizations during photosynthesis with a time resolution down to seconds [4].
In the biosphere phototroph organisms developed various strategies for efficient capture and transformation of the solar energy into chemical energy. Higher plants, cyanobacteria and various algal cells developed thylakoid membrane – the most abundant membrane on earth – which has a crucial role in the primary steps of photosynthesis. This membrane separates two aqueous phase (the stroma and the lumen) and incorporates virtually all protein complexes involved in the light reactions of photosynthesis. The macroorganization of the thylakoids, which show significant variations among the different organisms, has a high flexibility and can be easily influenced by variations in the environmental parameters. This structural flexibility has a crucial role in the adaptation capabilities of the photosynthetic aparatii to the changing environment. Small angle neutron scattering, as a non invasive experimental method, which can also capitalize on the possibility of contrast variation, is an ideal tool for the study of these reorganizations. Our experiments allowed determination of characteristic repeat distances of thylakoid membranes isolated from plants, in cyanobacteria and in diatom, revealed their light-induced reversible reorganizations and helped to understand some of the driving forces for these mechanisms [1]. In diatoms we could connect the observed changes in the lamellar order of the membranes with changes in the long-range chiral order (measured by circular dichroism) of the incorporated chromophores [2]. We also followed the influence of external parameters as osmolarity, ionic strength or strong illumination on the periodicity of thylakoid membranes of higher plants [3]. SANS allowed to follow the kinetics of the membrane reorganizations during photosynthesis with a time resolution down to seconds [4].
Fig. 1: Scattering profile of thylakoid membranes isolated from tobacco leaves, suspended in 20 mM Tricine (pD 7.6), 5 mM MgCl2, 5 mM KCl and 0.4 M sorbitol in D2O. The Bragg peak of the multilamellar membrane system is visible around 0.02 Å-1. Membranes were oriented with an external magnetic field of 0.4 T field strength. Data was recorded with the 2D detector of the SANS-I instrument (SINQ). The instrument settings were: sample-to-detector distance = 11 m, collimation = 15 m and λ = 6 Å. Corresponding instrumental and empty cell background measurements are subtracted.
Photosystem II is the primary protein complex in the photosynthetic electrontransport chain which oxidizes water molecules on the luminal side of the thylakoid membranes with the driving force of the absorbed photons. We applied elastic incoherent neutron scattering (EINS) for investigating the dynamics of Photosystem II containing membrane fragments around the physiological temperature range and reveal a transition which could be connected to the detachment of its oxygen evolving complex subunit from the membrane [5].
Bacteriorhodopsin is the simplest known biological pump in biological systems. We performed dynamical characterization of bacteriorhodopsin containing purple membranes in the physiological temperature range in the presence of high concentration of different salts (representative members of the Hofmeister series). Our EINS measurements helped to understand how conformational fluctuations in the bacteriorhodopsin molecule are affected by the presence of these salts [6].
These experiments, apart from answering questions in the structure and dynamics of energy converting biological membranes also demonstrate the power of neutron scattering for the study of complex biological systems. The studies were performed in collaboration with the Institut Laue-Langevin (Grenoble, France), Wigner Research Centre for Physics (Budapest, Hungary), Biological Research Center (Szeged, Hungary), Roskilde University (Roskilde, Denmark), University of Tartu (Tartu, Estonia) and the Institute of Biophysics and Biomedical Engineering (Sofia, Bulgaria).
References
Photosystem II is the primary protein complex in the photosynthetic electrontransport chain which oxidizes water molecules on the luminal side of the thylakoid membranes with the driving force of the absorbed photons. We applied elastic incoherent neutron scattering (EINS) for investigating the dynamics of Photosystem II containing membrane fragments around the physiological temperature range and reveal a transition which could be connected to the detachment of its oxygen evolving complex subunit from the membrane [5].
Bacteriorhodopsin is the simplest known biological pump in biological systems. We performed dynamical characterization of bacteriorhodopsin containing purple membranes in the physiological temperature range in the presence of high concentration of different salts (representative members of the Hofmeister series). Our EINS measurements helped to understand how conformational fluctuations in the bacteriorhodopsin molecule are affected by the presence of these salts [6].
These experiments, apart from answering questions in the structure and dynamics of energy converting biological membranes also demonstrate the power of neutron scattering for the study of complex biological systems. The studies were performed in collaboration with the Institut Laue-Langevin (Grenoble, France), Wigner Research Centre for Physics (Budapest, Hungary), Biological Research Center (Szeged, Hungary), Roskilde University (Roskilde, Denmark), University of Tartu (Tartu, Estonia) and the Institute of Biophysics and Biomedical Engineering (Sofia, Bulgaria).
References
- [1] Nagy G, et al. (2011) Reversible membrane reorganizations during photosynthesis in vivo: revealed by small-angle neutron scattering. Biochem J 436(2):225-230.
- [2] Nagy G, et al. (2012) Modulation of the multilamellar membrane organization and of the chiral macrodomains in the diatom Phaeodactylum tricornutum revealed by small-angle neutron scattering and circular dichroism spectroscopy. Photosynth Res 111(1-2):71-79.
- [3] Posselt D, et al. (2012) Small-angle neutron scattering study of the ultrastructure of chloroplast thylakoid membranes - Periodicity and structural flexibility of the stroma lamellae. Biochim Biophys Acta Bioenerg 1817(8):1220-1228.
- [4] Nagy G, et al. Kinetics of structural reorganizations in multilamellar photosynthetic membranes monitored by small angle neutron scattering. submitted.
- [5] Nagy G, et al. (2012) Dynamic properties of photosystem II membranes at physiological temperatures characterized by elastic incoherent neutron scattering. Increased flexibility associated with the inactivation of the oxygen evolving complex. Photosynth Res 111(1-2):113-124.
- [6] Szalontai B, et al. Hofmeister ions control protein dynamics. prepared for submission.