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• W2028242510 abstract "Photosystem I (PSI) is a membrane protein complex that catalyzes sunlight-driven transmembrane electron transfer as part of the photosynthetic machinery. Photosynthetic organisms appeared on the Earth about 3.5 billion years ago and provided an essential source of potential energy for the development of life. During the course of evolution, these primordial organisms were phagocytosed by more sophisticated eukaryotic cells, resulting in the evolvement of algae and plants. Despite the extended time interval between primordial cyanobacteria and plants, PSI has retained its fundamental mechanism of sunlight conversion. Being probably the most efficient photoelectric apparatus in nature, PSI operates with a quantum efficiency close to 100%. However, adapting to different ecological niches necessitated structural changes in the PSI design. Based on the recently solved structure of plant PSI, which revealed a complex of 17 protein subunits and 178 prosthetic groups, we analyze the evolutionary development of PSI. In addition, some aspects of PSI structure determination are discussed. Photosystem I (PSI) is a membrane protein complex that catalyzes sunlight-driven transmembrane electron transfer as part of the photosynthetic machinery. Photosynthetic organisms appeared on the Earth about 3.5 billion years ago and provided an essential source of potential energy for the development of life. During the course of evolution, these primordial organisms were phagocytosed by more sophisticated eukaryotic cells, resulting in the evolvement of algae and plants. Despite the extended time interval between primordial cyanobacteria and plants, PSI has retained its fundamental mechanism of sunlight conversion. Being probably the most efficient photoelectric apparatus in nature, PSI operates with a quantum efficiency close to 100%. However, adapting to different ecological niches necessitated structural changes in the PSI design. Based on the recently solved structure of plant PSI, which revealed a complex of 17 protein subunits and 178 prosthetic groups, we analyze the evolutionary development of PSI. In addition, some aspects of PSI structure determination are discussed. Photosystem I (PSI) is a large membrane protein complex that catalyzes the first step of oxygenic photosynthesis performed by plants, green algae, and cyanobacteria. PSI captures sunlight through a highly sophisticated pigment network and uses the energy to perform light-driven transmembrane electron transfer. Being one of the most elaborated membrane complexes, PSI operates with the unprecedented photochemical quantum yield of close to 1.0 (Nelson and Yocum, 2006Nelson N. Yocum C. Structure and function of photosystems I and II.Annu. Rev. Plant Biol. 2006; 57: 521-565Crossref PubMed Scopus (314) Google Scholar). For this reason, it is regarded as the most efficient light capturing and energy conversion device in nature. As such, it is studied by many groups from a very wide spectrum of disciplines, providing attractive expectations for the sun energy utilization and manufacturing of photosensors in the future (Lewis, 2007Lewis N.S. Toward cost-effective solar energy use.Science. 2007; 315: 798-801Crossref PubMed Scopus (591) Google Scholar, Carmeli et al., 2007Carmeli I. Frolov L. Carmeli C. Richter S. Photovoltaic activity of photosystem I-based self-assembled monolayer.J. Am. Chem. Soc. 2007; 129: 12352-12353Crossref PubMed Scopus (50) Google Scholar, Terasaki et al., 2007Terasaki N. Yamamoto N. Tamada K. Hattori M. Hiraga T. Tohri A. Sato I. Enami I. Inoue Y. Yamanoi Y. et al.Biol.-photo sensor: cyanobacterial photosystem I coupled with transistor via molecular wire.Biochim. Biophys. Acta. 2007; 1767: 653-659Crossref PubMed Scopus (51) Google Scholar). Structurally, plant PSI consists of two membrane complexes: the core complex, also referred to as the reaction center (RC) complex, where the bulk of the light capturing and the charge separation reaction take place, and the light-harvesting complex I (LHCI), which serves as an additional antenna system that maximizes light harvesting by collecting solar radiation and transmitting the energy to the core complex (Chitnis, 2001Chitnis P.R. Photosystem I: function and physiology.Annu. Rev. Plant Physiol. Plant Mol. Biol. 2001; 52: 593-626Crossref PubMed Google Scholar). In this review, we refer to plant PSI as the PSI-LHCI supercomplex. The supercomplex is composed of 19 currently known protein subunits and approximately 200 noncovalently bound cofactors spread between the core complex and the LHCI (Jensen et al., 2007Jensen P.E. Bassi R. Boekema E.J. Dekker J.P. Jansson S. Leister D. Robinson C. Scheller H.V. Structure, function and regulation of plant photosystem I.Biochim. Biophys. Acta. 2007; 1767: 335-352Crossref PubMed Scopus (74) Google Scholar). Plant PSI-LHCI is much larger than its cyanobacterial counterpart, which doesn't contain LHCI and consists of 12 subunits and 127 cofactors (Jordan et al., 2001Jordan P. Fromme P. Witt H.T. Klukas O. Saenger W. Krauß N. Three-dimensional structure of cyanobacterial photosystem I at 2.5 A resolution.Nature. 2001; 411: 909-917Crossref PubMed Scopus (1299) Google Scholar, Fromme et al., 2001Fromme P. Jordan P. Krauß N. Structure of photosystem I.Biochim. Biophys. Acta. 2001; 1507: 5-31Crossref PubMed Scopus (231) Google Scholar). Of particular note is that in unicellular green algae, whose lineage diverged from land plants over 1 billion years ago, LHCI is about three times larger than that of higher plants (Germano et al., 2002Germano M. Yakushevska A.E. Keegstra W. van Gorkom H.J. Dekker J.P. Boekema E. Supramolecular organization of photosystem I and light-harvesting complex I in Chlamydomonas reinhardtii.FEBS Lett. 2002; 525: 121-125Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar, Kargul et al., 2003Kargul J. Nield J. Barber J. Three-dimensional reconstruction of a light-harvesting complex I-photosystem I (LHCI-PSI) supercomplex from the green alga Chlamydomonas reinhardtii –insights into light harvesting for PSI.J. Biol. Chem. 2003; 278: 16135-16141Crossref PubMed Scopus (79) Google Scholar). In this paper, we will review the structural modality of PSI during 3.5 billion years of evolution, from primordial deep ocean habitants to sophisticated green plants, and point out its contribution for development of the terrestrial life on Earth. Functionally, PSI catalyzes the light-driven electron transfer from the soluble electron carrier plastocyanin, located at the lumenal side (inside) of the thylakoid membrane, to ferredoxin, at the stromal side (outside) of the natural photosynthetic membrane (Bengis and Nelson, 1977Bengis C. Nelson N. Subunit structure of chloroplast photosystem I reaction center.J. Biol. Chem. 1977; 252: 4564-4569Abstract Full Text PDF PubMed Google Scholar). This multistep electron transfer is launched by PSI through a series of redox cofactors located in the heart of the core complex, the electron transport chain (ETC). The ETC consists of organic and inorganic portions. The organic portion is represented by six chlorophylls and two phylloquinones, arranged in two branches, and the nonorganic portion is composed of three Fe4S4 clusters. The excitation energy for the function of the ETC is delivered from the LHCI via the core complex pigment (chlorophylls and carotenoids) network. A fascinating feature of the PSI ETC is that it generates probably the most powerful reductant of any of the natural systems studied thus far (Brettel and Leibl, 2001Brettel K. Leibl W. Electron transfer in photosystem I.Biochim. Biophys. Acta. 2001; 1507: 100-114Crossref PubMed Scopus (137) Google Scholar). Many spectroscopy techniques, including electron paramagnetic resonance and Fourier transform infrared spectroscopy, as well as other methods that measure changes in optical absorption, have provided a wealth of information regarding the key elements of PSI energy conversion (Stehlik, 2006Stehlik D. Transient EPR spectroscopy as applied to light-induced functional intermediates along the electron transfer pathway in photosystem I.in: Golbeck J. Photosystem I: The Light-Driven Plastocyanin:Ferredoxin Oxidoreductase. Springer, Dordrecht2006: 361-386Google Scholar, Thurnauer et al., 2006Thurnauer M. Poluektov O. Kothe G. High-field EPR studies of electron transfer intermediates in photosystem I.in: Golbeck J. Photosystem I: The Light-Driven Plastocyanin:Ferredoxin Oxidoreductase. Springer, Dordrecht2006: 339-360Google Scholar, Breton, 2006Breton J. FTIR studies of the primary electron donor, P700.in: Golbeck J. Photosystem I: The Light-Driven Plastocyanin:Ferredoxin Oxidoreductase. Springer, Dordrecht2006: 271-290Google Scholar, Lubitz, 2006Lubitz W. EPR studies of the primary electron donor P700 in photosystem I.in: Golbeck J. Photosystem I: The Light-Driven Plastocyanin:Ferredoxin Oxidoreductase. Springer, Dordrecht2006: 245-269Google Scholar, Rappaport, 2006Rappaport F. Optical measurements of secondary electron transfer in photosystem I.in: Golbeck J. Photosystem I: The Light-Driven Plastocyanin:Ferredoxin Oxidoreductase. Springer, Dordrecht2006: 224-244Google Scholar, Savikhin, 2006Savikhin S. Ultrafast optical spectroscopy of photosystem I.in: Golbeck J. Photosystem I: The Light-Driven Plastocyanin:Ferredoxin Oxidoreductase. Springer, Dordrecht2006: 155-175Google Scholar). However, from a structural biology point of view, the atomic-resolution model, which provides a template for understanding the mechanism of the unprecedented high quantum yield of PSI in light capture and electron transfer, remains the ultimate goal. Recently, we made significant progress toward this goal by solving the intact structure of the plant PSI-LHCI supercomplex at 3.4 Å resolution (Amunts et al., 2007Amunts A. Drory O. Nelson N. The structure of a plant photosystem I supercomplex at 3.4 Å resolution.Nature. 2007; 447: 58-63Crossref PubMed Scopus (216) Google Scholar). This three-dimensional description laid the foundation for further structural analysis, which is presented in this review. However, we will first describe briefly how the structure of plant PSI was achieved and discuss some of the biochemical and crystallographic aspects of X-ray crystal structure determination. The plant PSI core was isolated from Swiss chard leaves, purified, and characterized with respect to subunit composition for the first time in 1975 (Bengis and Nelson, 1975Bengis C. Nelson N. Purification and properties of the photosystem I reaction center from chloroplasts.J. Biol. Chem. 1975; 250: 2783-2788Abstract Full Text PDF PubMed Google Scholar). It took another 5 years before the first report of a purified intact PSI-LHCI supercomplex from pea plants was published (Mullet et al., 1980Mullet J.E. Burke J.J. Arntzen C.J. Chlorophyll proteins of photosystem I.Plant Physiol. 1980; 65: 814-822Crossref PubMed Google Scholar). Since then, PSI has presented a formidable challenge to structural biologists. A milestone of these efforts was the elucidation of the X-ray structure of the purple bacterial RC by Deisenhofer et al., 1985Deisenhofer J. Epp O. Miki K. Huber R. Michel H. Structure of the protein subunits in the photosynthetic reaction centre of Rhodopseudomonas viridis at 3 Å resolution.Nature. 1985; 318: 618-624Crossref PubMed Scopus (1512) Google Scholar. This significant achievement represented a turning point in membrane protein crystallization history and spurred many structural biologists to pursue the structure of large membrane proteins. For the recent review of structure determination of photosynthetic complexes, please see Allen et al. (2009)Allen J.P. Seng C. Larson C. Structures of proteins and cofactors: X-ray crystallography.Photosynth. Res. 2009; (in press. Published online March 26, 2009)https://doi.org/10.1007/s11120-009-9416-4Crossref Scopus (3) Google Scholar. With regard to PSI isolated from higher plants, the first direct significant structural information was obtained by electron microscopy of single particles and cryoelectron crystallography of 2D crystals. Single particle analysis showed monomeric particles without apparent symmetry (Boekema et al., 1990Boekema E. Wynn R. Malkin R. The structure of spinach photosystem I studied by electron microscopy.Biochim. Biophys. Acta. 1990; 1017: 49-56Crossref Scopus (39) Google Scholar). Further 2D crystallization of spinach PSI yielded a projection map of about 25 Å resolution (Kitmitto et al., 1998Kitmitto A. Mustafa A.O. Holzenburg A. Ford R.C. Three-dimensional structure of higher plant photosystem I determined by electron crystallography.J. Biol. Chem. 1998; 273: 29592-29599Crossref PubMed Scopus (22) Google Scholar), revealing the overall shape of the complex with a high-density domain on the stromal side, which was hypothesized to contain extrinsic polypeptides. Additional studies have suggested that these stromal polypeptides are a binding site of the electron acceptor ferredoxin (Ruffle et al., 2000Ruffle S.V. Mustafa A.O. Kitmitto A. Holzenburg A. Ford R.C. The location of the mobile electron carrier ferredoxin in vascular plant photosystem I.J. Biol. Chem. 2000; 275: 36250-36255Crossref PubMed Scopus (12) Google Scholar) and also proposed a docking region for the mobile electron donor plastocyanin on the opposite side of the complex (Ruffle et al., 2002Ruffle S.V. Mustafa A.O. Kitmitto A. Holzenburg A. Ford R.C. The location of plastocyanin in vascular plant photosystem I.J. Biol. Chem. 2002; 277: 25692-25696Crossref PubMed Scopus (7) Google Scholar). Importantly, these studies of plant PSI could not have occurred without a significant progress in the cyanobacterial PSI structure elucidation (Krauß et al., 1993Krauß N. Hinrichs W. Witt I. Fromme P. Pritzkow W. Dauter Z. Betzel C. Wilson K.S. Witt H.T. Saenger W. Three-dimensional structure of system I of photosynthesis at 6Å resolution.Nature. 1993; 361: 326-331Crossref Google Scholar, Krauß et al., 1996Krauß N. Schubert W.D. Klukas O. Fromme P. Witt H.T. Saenger W. Photosystem I at 4Å resolution represents the first structural model of a joint photosynthetic reaction centre and core antenna system.Nat. Struct. Biol. 1996; 3: 965-973Crossref PubMed Scopus (282) Google Scholar, Schubert et al., 1997Schubert W.D. Klukas O. Krauß N. Saenger W. Fromme P. Witt H.T. Photosystem I of Synechococcus elongatus at 4 Å resolution: comprehensive structure analysis.J. Mol. Biol. 1997; 272: 741-769Crossref PubMed Scopus (210) Google Scholar, Klukas et al., 1999aKlukas O. Schubert W.D. Jordan P. Krauß N. Fromme P. Witt H.T. Saenger W. Localization of two phylloquinones, QK and QK′, in an improved electron density map of photosystem I at 4-Å resolution.J. Biol. Chem. 1999; 274: 7361-7367Crossref PubMed Scopus (67) Google Scholar, Klukas et al., 1999bKlukas O. Schubert W.D. Jordan P. Krauß N. Fromme P. Witt H.T. Saenger W. Photosystem I, an improved model of the stromal subunits PsaC, PsaD, and PsaE.J. Biol. Chem. 1999; 274: 7351-7360Crossref PubMed Scopus (70) Google Scholar). An additional important step toward a more detailed PSI model was achieved by comparing projection maps from different species (plants, algae, and cyanobacteria). This yielded insights into the arrangement of antenna proteins and the subunit composition of the PSI core (Boekema et al., 2001aBoekema E.J. Hifney A. Yakushevska A.E. Piotrowski M. Keegstra W. Berry S. Michel K.P. Pistorius E.K. Kruip J. A giant chlorophyll–protein complex induced by iron deficiency in cyanobacteria.Nature. 2001; 412: 745-748Crossref PubMed Scopus (196) Google Scholar, Germano et al., 2002Germano M. Yakushevska A.E. Keegstra W. van Gorkom H.J. Dekker J.P. Boekema E. Supramolecular organization of photosystem I and light-harvesting complex I in Chlamydomonas reinhardtii.FEBS Lett. 2002; 525: 121-125Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar, Kargul et al., 2003Kargul J. Nield J. Barber J. Three-dimensional reconstruction of a light-harvesting complex I-photosystem I (LHCI-PSI) supercomplex from the green alga Chlamydomonas reinhardtii –insights into light harvesting for PSI.J. Biol. Chem. 2003; 278: 16135-16141Crossref PubMed Scopus (79) Google Scholar, Vacha et al., 2005Vacha F. Bumba L. Kaftan D. Vacha M. Microscopy and single molecule detection in photosynthesis.Micron. 2005; 36: 483-502Crossref PubMed Scopus (13) Google Scholar). On the basis of these studies it was concluded that LHCI binds to the core on only one side of the complex. In spite of these breakthroughs, the X-ray structural analysis of plant PSI remained elusive for years, due to the complex's size and location in a membranous environment. To avoid any disturbances during the crystal growth process, researchers even attempted to crystallize cyanobacterial PSI under microgravity conditions in outer space, during four missions of the Space Shuttle Columbia, from 1995 to 2003 (Fromme and Mathis, 2004Fromme P. Mathis P. Unraveling the photosystem I reaction center: a history, or the sum of many efforts.Photosynth. Res. 2004; 80: 109-124Crossref PubMed Scopus (23) Google Scholar). The two major breakthroughs in unraveling PSI were the elucidations of the 2.5 Å resolution X-ray crystal structure of the trimeric PSI from cyanobacteria (Thermosynechococcus elongatus) (Jordan et al., 2001Jordan P. Fromme P. Witt H.T. Klukas O. Saenger W. Krauß N. Three-dimensional structure of cyanobacterial photosystem I at 2.5 A resolution.Nature. 2001; 411: 909-917Crossref PubMed Scopus (1299) Google Scholar) and the 4.4 Å resolution intact PSI-LHCI supercomplex from pea (Pisum sativum) (Ben-Shem et al., 2003Ben-Shem A. Frolow F. Nelson N. Crystal structure of plant photosystem I.Nature. 2003; 426: 630-635Crossref PubMed Scopus (431) Google Scholar). For the first time, the subunit composition, as well as the architecture of the cofactors and the antenna system, was identified. Plant PSI-LHCI was not only the first structure of a plant membrane protein to be solved by X-ray crystallography, it was also the first membrane supercomplex to be solved by this method, and it provided additional intriguing insights to those yielded by its cyanobacterial counterpart. However, the 4.4 Å resolution was limited to the main structural elements only, leaving some uncertainty with regard to important features. In-depth characterization of the protein samples and detailed analysis of purification procedures (Amunts et al., 2005Amunts A. Ben-Shem A. Nelson N. Solving the structure of plant photosystem I: biochemistry is vital.Photochem. Photobiol. Sci. 2005; 4: 1011-1015Crossref PubMed Scopus (17) Google Scholar) enabled optimization of crystallization conditions, which yielded improved crystal quality, resulting in the recent structural model at 3.4 Å resolution (Amunts et al., 2007Amunts A. Drory O. Nelson N. The structure of a plant photosystem I supercomplex at 3.4 Å resolution.Nature. 2007; 447: 58-63Crossref PubMed Scopus (216) Google Scholar). The current crystal structure confirmed essential findings from the previous, low-resolution model and at the same time revealed additional insights that had not been previously possible. However, the 3.4 Å resolution data of plant PSI-LHCI still has severe limitations. The structural data for the peripheral areas remain poor and don't provide structural legitimacy for fine details; thus, they should be used carefully because movement of polypeptides or cofactors could lead to erroneous conclusions. Plant PSI-LHCI structure determination was complicated by a number of factors, including dependence on plant growth conditions, elasticity of the supercomplex, interaction of crystals with the plastic of the wells, and crystal polymorphism. We analyzed every stage of the process, from plant germination to evaluation of the damage caused to crystals by exposure to X-rays. Among others, it was found that the cryoprotecting solution has a major effect on the diffraction quality. The significant improvement in the diffraction quality was achieved by a controlled dehydration process. Dehydration was performed by soaking the crystals in gradually increasing concentrations of the precipitating agent. Once the crystals had achieved the maximum size at the crystallization droplet containing ∼5% PEG 6000, they were relocated over a reservoir with up to 40% PEG 6000 throughout several intermediate steps, each one with an incubation time of up to 24 hr. This postcrystallization soaking shrank crystals to the apparent minimum of variable unit-cell dimensions, decreasing the cell volume by about 30%, from 3.56 [m−8]3 to 2.4 [m−8]3. The final solvent content in the crystal was reduced to 48%, resulting in very dense crystal packing with close contacts between adjacent molecules, as shown in Figure 1. This procedure also reduced the level of crystal polymorphism, improving the reproducibility of better diffracting crystals. However, excess shrinkage could have lead to some distortions in the structure of peripheral portions of the supercomplex. In spite of all of these improvements, most of the plant PSI-LHCI crystals did not diffract below 6 Å and solving the intact crystal structure by X-ray analysis required screening of approximately 10,000 crystals over the last 4 years. Hundreds of crystals had to be screened on every synchrotron visit to identify those that diffracted substantially better than others. Moreover, severe radiation damage allowed only 10–20 frames to be collected per portion of the crystal. This, in conjunction with relatively small crystal sizes, did not permit a complete data set collection from a single crystal. Fine beam focusing was necessary to reduce radiation damage and to allow shifting of the X-ray beam a few times per crystal. An additional major problem was crystal polymorphism; unit-cell size varied by as much as 7° in one angle and up to 10 Å in each dimension. Polymorphism was not restricted to between different crystals, but the diffraction parameters varied greatly within the same crystals as well. This required collection of large amounts of data to allow the completion of one single full set of data with isomorphous parameters and reasonable statistics. Eventually, data from ten different crystals had to be merged for a sufficient structure determination with reasonable crystallographic statistics. After each cycle of refinement, the model was manually rebuilt on the basis of the resultant 2F0–FC maps, validation restrictions, biochemical evidence, and common sense. Restrained individual B factor refinement was not performed until the last cycle. Conclusively, iterative cycles of model building and refinement yielded an almost 30,000 atom model, with considerable Rcryst/Rfree values (35%/40%), including the newly identified 9.5 kDa subunit (PsaN). The final model of 2909 residues, 168 chlorophylls, 3 Fe4S4 clusters, and 5 carotenoids provides the most complete available description of a plant PSI-LHCI supercomplex. However, even at 3.4 Å resolution, several carotenoids and even polypeptides escaped detection; the entire supercomplex is expected to contain over 20% more atoms. Thus, the atomic-resolution model remains highly desired. Plant PSI-LHCI occurs as a monomer in the crystalline state as well as in vivo. The overall structure, shown in Figure 2, has a maximal height of ∼100 Å and diameter of ∼185 Å and ∼150 Å. In the electron density map, 17 biochemically characterized and sequenced protein subunits were identified. Crystallized PSI-LHCI supercomplex contains 13 protein subunits that transverse the thylakoid membrane (PsaA, PsaB, PsaF, PsaG, PsaH, PsaI, PsaJ, PsaK, PsaL, and Lhca1–4) comprising 45 transmembrane helices, 3 stroma-exposed subunits (PsaC, PsaD, and PsaE), and 1 luminal subunit (PsaN). 168 chlorophylls were identified in the structure; for 65 of them, the orientations of the head groups were determined, leading to the assignment of the QX and QY transition dipolar moments. In addition, the three Fe4S4 clusters, two phylloquinones, and five carotenoids were modeled. The overall of 178 cofactors located in plant PSI-LHCI contributes about 30% of the total molecular mass of ∼600 kDa. Apart from the functional importance of numerous cofactors, they play an important part in the structural integrity of the complex. The role of the carotenoids in photosynthesis is more complex compared to other prosthetic groups of PSI-LHCI. There are at least three main functions of carotenoids, light harvesting, photoprotection, and structure stabilization, which were excellently reviewed by Frank and Cogdell, 1996Frank H. Cogdell R.J. Carotenoids in photosynthesis.Photochem. Photobiol. 1996; 63: 257-264Crossref PubMed Google Scholar. However, until most of the expected ∼30 carotenoids are assigned it will not be fruitful to discuss their functional arrangement in plant PSI. PSI from pea plants was isolated, purified, and crystallized as the intact supercomplex of the core complex and LHCI complex (PSI-LHCI) that captures light and guides its energy to the reactive site. In the following sections, we explore key structural and functional properties of the two complexes in the context of evolutionary forces. In general, the core complex of plant PSI retains the protein backbone and coordination sites of chlorophylls at locations similar to those found in cyanobacterial PSI (Jordan et al., 2001Jordan P. Fromme P. Witt H.T. Klukas O. Saenger W. Krauß N. Three-dimensional structure of cyanobacterial photosystem I at 2.5 A resolution.Nature. 2001; 411: 909-917Crossref PubMed Scopus (1299) Google Scholar, Fromme et al., 2001Fromme P. Jordan P. Krauß N. Structure of photosystem I.Biochim. Biophys. Acta. 2001; 1507: 5-31Crossref PubMed Scopus (231) Google Scholar, Amunts and Nelson, 2008Amunts A. Nelson N. Functional organization of a plant photosystem I: evolution of a highly efficient photochemical machine.Plant Physiol. Biochem. 2008; 46: 228-237Crossref PubMed Scopus (24) Google Scholar). However, more than a billion years of separate evolution has shaped some key modifications of these representatives of two kingdoms as dictated by their different ecological niches and will be discussed here. The central part of the core complex is formed by the heterodimer of the two large transmembrane protein subunits PsaA and PsaB, comprising 22 transmembrane helices. This fundamental core evolved from a homodimeric ancestor (Tittgen et al., 1986Tittgen J. Hermans J. Steppuhn J. Jansen T. Jansson C. Andersson B. Nechushtai R. Nelson N. Herrmann R.G. Isolation of cDNA clones for fourteen nuclear-encoded thylakoid membrane proteins.Mol. Gen. Genet. 1986; 204: 258-265Crossref Scopus (20) Google Scholar, Büttner et al., 1992Büttner M. Xie D.-L. Nelson H. Pinther W. Hauska G. Nelson N. The photosystem I-like P840-reaction center of green S-bacteria is a homodimer.Biochim. Biophys. Acta. 1992; 1101: 154-156Crossref PubMed Scopus (35) Google Scholar, Liebl et al., 1993Liebl U. Mockensturm-Wilson M. Trost J. Brune D. Blankenship R. Vermaas W. Single core polypeptide in the reaction center of the photosynthetic bacterium Heliobacillus mobilis: structural implications and relations to other photosystems.Proc. Natl. Acad. Sci. USA. 1993; 90: 7124-7128Crossref PubMed Google Scholar), originated from gene duplication of an ancestral gene (Blankenship, 1992Blankenship R.E. Origin and early evolution of photosynthesis.Photosynth. Res. 1992; 33: 91-111Crossref Scopus (207) Google Scholar, Ben-Shem et al., 2004Ben-Shem A. Frolow F. Nelson N. Evolution of photosystem I—from symmetry through pseudo-symmetry to asymmetry.FEBS Lett. 2004; 564: 274-280Abstract Full Text Full Text PDF PubMed Scopus (75) Google Scholar). The N termini of both subunits are stromally exposed, whereas the C termini are located on the lumenal side. The membrane integral parts preserve the local pseudosymmetry, which relates PsaA to PsaB and extends to chlorophyll locations as well. The loop regions contain short, 5–11 amino acid, helical elements, which also coordinate about 30 antenna chlorophylls. These loop regions on the lumenal side are generally more extended than the loops on the stromal side, shielding the cofactors from the aqueous phase. The PsaA/B heterodimer coordinates most of the ETC cofactors and overall 80 chlorophylls that function as the intrinsic light-harvesting antennae. The stromal loops of PsaA and PsaB associate the three stromal subunits PsaC, PsaD, and PsaE, which are closely linked to one another, forming a binding groove for the electron acceptor ferredoxin. Flash absorption spectroscopy has revealed two different kinetic phases in the reduction of soluble ferredoxin by PSI, with half-times of approximately 500 ns and 20 μs (Fischer et al., 1999Fischer N. Sétif P. Rochaix J.-D. Site-directed mutagenesis of the PsaC subunit of photosystem I. F(b) is the cluster interacting with soluble ferredoxin.J. Biol. Chem. 1999; 274: 23333-23340Crossref PubMed Scopus (33) Google Scholar). Thus, the existence of two distinct ferredoxin binding states, a tight and a loose bound, was suggested. Figure 3 depicts these putative docking sites, based on site-directed mutagenesis studies (Hanley et al., 1996Hanley J. Sétif P. Bottin H. Lagoutte B. Mutagenesis of photosystem I in the region of the ferredoxin cross-linking site: modifications of positively charged amino acids.Biochemistry. 1996; 35: 8563-8571Crossref PubMed Scopus (36) Google Scholar, Fischer et al., 1998Fischer N. Hippler M. Sétif P. Jacquot J.P. Rochaix J.-D. The PsaC subunit of photosystem I provides an essential lysine residue for fast electron transfer to ferredoxin.EMBO J. 1998; 17: 849-858Crossref PubMed Scopus (54) Google Scholar, Fischer et al., 1999Fischer N. Sétif P. Rochaix J.-D. Site-directed mutagenesis of the PsaC subunit of photosyst" @default.
• W2028242510 created "2016-06-24" @default.
• W2028242510 creator A5078387949 @default.
• W2028242510 creator A5085637404 @default.
• W2028242510 date "2009-05-01" @default.
• W2028242510 modified "2023-10-16" @default.
• W2028242510 title "Plant Photosystem I Design in the Light of Evolution" @default.
• W2028242510 cites W133141825 @default.
• W2028242510 cites W1506353539 @default.
• W2028242510 cites W1532877896 @default.
• W2028242510 cites W1538055033 @default.
• W2028242510 cites W1547252610 @default.
• W2028242510 cites W1550809931 @default.
• W2028242510 cites W1561216036 @default.
• W2028242510 cites W1561945007 @default.
• W2028242510 cites W1654006715 @default.
• W2028242510 cites W1820891978 @default.
• W2028242510 cites W1965993257 @default.
• W2028242510 cites W1968122402 @default.
• W2028242510 cites W1969771592 @default.
• W2028242510 cites W1969896214 @default.
• W2028242510 cites W1970487315 @default.
• W2028242510 cites W1970736469 @default.
• W2028242510 cites W1973447343 @default.
• W2028242510 cites W1973534141 @default.
• W2028242510 cites W1975418426 @default.
• W2028242510 cites W1977780211 @default.
• W2028242510 cites W1983562517 @default.
• W2028242510 cites W1984100061 @default.
• W2028242510 cites W1988950854 @default.
• W2028242510 cites W1990148094 @default.
• W2028242510 cites W1990547652 @default.
• W2028242510 cites W1991739777 @default.
• W2028242510 cites W1992236822 @default.
• W2028242510 cites W1992858669 @default.
• W2028242510 cites W1995539264 @default.
• W2028242510 cites W1999633187 @default.
• W2028242510 cites W2001621734 @default.
• W2028242510 cites W2002338734 @default.
• W2028242510 cites W2004218904 @default.
• W2028242510 cites W2007011722 @default.
• W2028242510 cites W2007176314 @default.
• W2028242510 cites W2007329635 @default.
• W2028242510 cites W2008567589 @default.
• W2028242510 cites W2009524403 @default.
• W2028242510 cites W2009783969 @default.
• W2028242510 cites W2009852647 @default.
• W2028242510 cites W2013202455 @default.
• W2028242510 cites W2013278565 @default.
• W2028242510 cites W2014604680 @default.
• W2028242510 cites W2015249872 @default.
• W2028242510 cites W2015358843 @default.
• W2028242510 cites W2015882075 @default.
• W2028242510 cites W2016185790 @default.
• W2028242510 cites W2019704721 @default.
• W2028242510 cites W2020345264 @default.
• W2028242510 cites W2025262653 @default.
• W2028242510 cites W2026118407 @default.
• W2028242510 cites W2028262546 @default.
• W2028242510 cites W2028637545 @default.
• W2028242510 cites W2029186320 @default.
• W2028242510 cites W2030074614 @default.
• W2028242510 cites W2031295102 @default.
• W2028242510 cites W2031933160 @default.
• W2028242510 cites W2032247127 @default.
• W2028242510 cites W2032329779 @default.
• W2028242510 cites W2034459904 @default.
• W2028242510 cites W2035215142 @default.
• W2028242510 cites W2036753426 @default.
• W2028242510 cites W2038498610 @default.
• W2028242510 cites W2040739110 @default.
• W2028242510 cites W2049288502 @default.
• W2028242510 cites W2050630648 @default.
• W2028242510 cites W2050752342 @default.
• W2028242510 cites W2052989605 @default.
• W2028242510 cites W2053092060 @default.
• W2028242510 cites W2054363495 @default.
• W2028242510 cites W2055470404 @default.
• W2028242510 cites W2058196193 @default.
• W2028242510 cites W2062028223 @default.
• W2028242510 cites W2062444386 @default.
• W2028242510 cites W2063209910 @default.
• W2028242510 cites W2064955108 @default.
• W2028242510 cites W2065510140 @default.
• W2028242510 cites W2065894128 @default.
• W2028242510 cites W2067291386 @default.
• W2028242510 cites W2067974230 @default.
• W2028242510 cites W2071074910 @default.
• W2028242510 cites W2072665786 @default.
• W2028242510 cites W2072756678 @default.
• W2028242510 cites W2072811492 @default.
• W2028242510 cites W2073915314 @default.
• W2028242510 cites W2075755227 @default.
• W2028242510 cites W2080226828 @default.
• W2028242510 cites W2080876805 @default.
• W2028242510 cites W2084414009 @default.
• W2028242510 cites W2085396909 @default.
• W2028242510 cites W2086302101 @default.

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