Structure and Function of Intact Photosystem 1 Monomers from the Cyanobacterium Thermosynechococcus elongatus

Plant Biochemistry, Ruhr University Bochum, 44780 Bochum, Germany.
Biochemistry (Impact Factor: 3.02). 04/2010; 49(23):4740-51. DOI: 10.1021/bi901807p
Source: PubMed


Until now, the functional and structural characterization of monomeric photosystem 1 (PS1) complexes from Thermosynechococcus elongatus has been hampered by the lack of a fully intact PS1 preparation; for this reason, the three-dimensional crystal structure at 2.5 A resolution was determined with the trimeric PS1 complex [Jordan, P., et al. (2001) Nature 411 (6840), 909-917]. Here we show the possibility of isolating from this cyanobacterium the intact monomeric PS1 complex which preserves all subunits and the photochemical activity of the isolated trimeric complex. Moreover, the equilibrium between these complexes in the thylakoid membrane can be shifted by a high-salt treatment in favor of monomeric PS1 which can be quantitatively extracted below the phase transition temperature. Both monomers and trimers exhibit identical posttranslational modifications of their subunits and the same reaction centers but differ in the long-wavelength antenna chlorophylls. Their chlorophyll/P700 ratio (108 for the monomer and 112 for the trimer) is slightly higher than in the crystal structure, confirming mild preparation conditions. Interaction of antenna chlorophylls of the monomers within the trimer leads to a larger amount of long-wavelength chlorophylls, resulting in a higher photochemical activity of the trimers under red or far-red illumination. The dynamic equilibrium between monomers and trimers in the thylakoid membrane may indicate a transient monomer population in the course of biogenesis and could also be the basis for short-term adaptation of the cell to changing environmental conditions.

Download full-text


Available from: Bettina Warscheid
  • Source
    • "While oligomerization of autonomous monomeric complexes into dimers and trimers is a widespread principle for bioenergetic complexes of the photosynthetic electron transport chain, dimerization of the b 6 f complex is mandatory for its catalytic function (Breyton et al., 1997;Dietrich and Kühlbrandt, 1999). In contrast to PSI and PSII, which show high electron transport activities also as monomers (Takahashi et al., 2009;Watanabe et al., 2009;El-Mohsnawy et al., 2010), monomeric b 6 f is structurally impaired and functionally inactive (Breyton et al., 1997;Cramer et al., 2005). The three-dimensional structure indicates why the dimerization of this complex is important for stability and functionality. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The cyanobacterial cytochrome b6f complex is central for the coordination of photosynthetic and respiratory electron transport and also for the balance between linear and cyclic electron transport. The development of a purification strategy for a highly active dimeric b6f complex from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 enabled characterization of the structural and functional role of the small subunit PetP in this complex. Moreover, the efficient transformability of this strain allowed the generation of a ΔpetP mutant. Analysis on the whole-cell level by growth curves, photosystem II light saturation curves, and P700(+) reduction kinetics indicate a strong decrease in the linear electron transport in the mutant strain versus the wild type, while the cyclic electron transport via photosystem I and cytochrome b6f is largely unaffected. This reduction in linear electron transport is accompanied by a strongly decreased stability and activity of the isolated ΔpetP complex in comparison with the dimeric wild-type complex, which binds two PetP subunits. The distinct behavior of linear and cyclic electron transport may suggest the presence of two distinguishable pools of cytochrome b6f complexes with different functions that might be correlated with supercomplex formation.
    Full-text · Article · Aug 2014 · The Plant Cell
  • Source
    • "clusters, 4 lipids, and ~200 water molecules. More recent work has indicated that the trimer may contain over 330 chlorophyll molecules [47]. In addition to the high-resolution X-ray structure of PSI, there are many TEM single particle structures [48] [49] and even some high-resolution AFM structures of the PSI complex in native membranes [50] [51]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Oxygenic photosynthesis is driven via sequential action of PSII and PSI reaction centers via the Z-scheme. Both of these pigment-membrane protein complexes are found in cyanobacteria, algae, and plants. Unlike PSII, PSI is remarkably stable and does not undergo limiting photo-damage. This stability, as well as other fundamental structural differences, makes PSI the most attractive reaction centers for applied photosynthetic applications. These applied applications exploit the efficient light harvesting and high quantum yield of PSI where the isolated PSI particles are redeployed providing electrons directly as a photocurrent or, via a coupled catalyst to yield H2. Recent advances in molecular genetics, synthetic biology, and nanotechnology have merged to allow PSI to be integrated into a myriad of biohybrid devices. In photocurrent producing devices, PSI has been immobilized onto various electrode substrates with a continuously evolving toolkit of strategies and novel reagents. However, these innovative yet highly variable designs make it difficult to identify the rate-limiting steps and/or components that function as bottlenecks in PSI-biohybrid devices. In this study we aim to highlight these recent advances with a focus on identifying the similarities and differences in electrode surfaces, immobilization/orientation strategies, and artificial redox mediators. Collectively this work has been able to maintain an annual increase in photocurrent density (A cm(-2)) of ~10-fold over the past decade. The potential drawbacks and attractive features of some of these schemes are also discussed with their feasibility on a large-scale. As an environmentally benign and renewable resource, PSI may provide a new sustainable source of bioenergy. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy.
    Full-text · Article · Jan 2014 · Biochimica et Biophysica Acta
  • Source
    • "Monomeric PSI complexes have fewer protein subunits (12) but more chlorophylls (96) than PSII [6]. Cyanobacterial PSI complexes have been found in trimeric and monomeric forms in vitro [2,6–8] and a particularly long-wavelength fluorescence emission form of PSI is found in some cyanobacteria, possibly representing a trimer [8] [9] [10], but trimeric PSI has never been observed in the crystal structure or BN protein gels in plants [11] [12]. PSI supercomplexes, which consist of trimeric PSI associated with IsiA proteins [13], have also been isolated from cyanobacteria. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The half-life times of photosystem I and II proteins were determined using (15)N-labeling and mass spectrometry. The half-life times (30-75h for photosystem I components and <1-11h for the large photosystem II proteins) were similar when proteins were isolated from monomeric vs. oligomeric complexes on Blue-Native gels, suggesting that the two forms of both photosystems can interchange on a timescale of <1h or that only one form of each photosystem exists in thylakoids in vivo. The half-life times of proteins associated with either photosystem generally were unaffected by the absence of Small Cab-like proteins.
    Full-text · Article · Dec 2011 · FEBS letters
Show more