Publications by authors named "Ido Caspy"

9 Publications

  • Page 1 of 1

Structure of plant photosystem I-plastocyanin complex reveals strong hydrophobic interactions.

Biochem J 2021 Jun;478(12):2371-2384

Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.

Photosystem I is defined as plastocyanin-ferredoxin oxidoreductase. Taking advantage of genetic engineering, kinetic analyses and cryo-EM, our data provide novel mechanistic insights into binding and electron transfer between PSI and Pc. Structural data at 2.74 Å resolution reveals strong hydrophobic interactions in the plant PSI-Pc ternary complex, leading to exclusion of water molecules from PsaA-PsaB/Pc interface once the PSI-Pc complex forms. Upon oxidation of Pc, a slight tilt of bound oxidized Pc allows water molecules to accommodate the space between Pc and PSI to drive Pc dissociation. Such a scenario is consistent with the six times larger dissociation constant of oxidized as compared with reduced Pc and mechanistically explains how this molecular machine optimized electron transfer for fast turnover.
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http://dx.doi.org/10.1042/BCJ20210267DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8238519PMC
June 2021

The structure of a triple complex of plant photosystem I with ferredoxin and plastocyanin.

Nat Plants 2020 10 5;6(10):1300-1305. Epub 2020 Oct 5.

Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel.

The ability of photosynthetic organisms to use sunlight as a sole source of energy is endowed by two large membrane complexes-photosystem I (PSI) and photosystem II (PSII). PSI and PSII are the fundamental components of oxygenic photosynthesis, providing oxygen, food and an energy source for most living organisms on Earth. Currently, high-resolution crystal structures of these complexes from various organisms are available. The crystal structures of megadalton complexes have revealed excitation transfer and electron-transport pathways within the various complexes. PSI is defined as plastocyanin-ferredoxin oxidoreductase but a high-resolution structure of the entire triple supercomplex is not available. Here, using a new cryo-electron microscopy technique, we solve the structure of native plant PSI in complex with its electron donor plastocyanin and the electron acceptor ferredoxin. We reveal all of the contact sites and the modes of interaction between the interacting electron carriers and PSI.
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http://dx.doi.org/10.1038/s41477-020-00779-9DOI Listing
October 2020

Structure and energy transfer pathways of the Dunaliella Salina photosystem I supercomplex.

Biochim Biophys Acta Bioenerg 2020 10 20;1861(10):148253. Epub 2020 Jun 20.

Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel. Electronic address:

Oxygenic photosynthesis evolved more than 3 billion years ago in cyanobacteria. The increased complexity of photosystem I (PSI) became apparent from the high-resolution structures that were obtained for the complexes that were isolated from various organisms, ranging from cyanobacteria to plants. These complexes are all evolutionarily linked. In this paper, the researchers have uncovered the increased complexity of PSI in a single organism demonstrated by the coexistance of two distinct PSI compositions. The Large Dunaliella PSI contains eight additional subunits, six in PSI core and two light harvesting complexes. Two additional chlorophyll a molecules pertinent for efficient excitation energy transfer in state II transition were identified in PsaL and PsaO. Short distances between these newly identified chlorophylls correspond with fast excitation transfer rates previously reported during state II transition. The apparent PSI conformations could be a coping mechanism for the high salinity.
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http://dx.doi.org/10.1016/j.bbabio.2020.148253DOI Listing
October 2020

Structure of a minimal photosystem I from the green alga Dunaliella salina.

Nat Plants 2020 03 2;6(3):321-327. Epub 2020 Mar 2.

Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel.

Solar energy harnessed by oxygenic photosynthesis supports most of the life forms on Earth. In eukaryotes, photosynthesis occurs in chloroplasts and is achieved by membrane-embedded macromolecular complexes that contain core and peripheral antennae with multiple pigments. The structure of photosystem I (PSI) comprises the core and light-harvesting (LHCI) complexes, which together form PSI-LHCI. Here we determined the structure of PSI-LHCI from the salt-tolerant green alga Dunaliella salina using X-ray crystallography and electron cryo-microscopy. Our results reveal a previously undescribed configuration of the PSI core. It is composed of only 7 subunits, compared with 14-16 subunits in plants and the alga Chlamydomonas reinhardtii, and forms the smallest known PSI. The LHCI is poorly conserved at the sequence level and binds to pigments that form new energy pathways, and the interactions between the individual Lhca1-4 proteins are weakened. Overall, the data indicate the PSI of D. salina represents a different type of the molecular organization that provides important information for reconstructing the plasticity and evolution of PSI.
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http://dx.doi.org/10.1038/s41477-020-0611-9DOI Listing
March 2020

Crystal Structure of Photosystem I Monomer From PCC 6803.

Front Plant Sci 2018 4;9:1865. Epub 2019 Jan 4.

Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel.

A single histidine addition to the C-terminus of PsaL of sp. PCC 6803 was previously reported by our lab to shift the trimer-to-monomer ratio of PSI in favor of the monomeric form. P700 re-reduction and NADP photo-reduction measurements of the PsaL strain show no effect on PSI activity in comparison to the WT trimeric PSI. Crystal structure of the PsaL monomeric PSI reveals several alterations that occurred in the trimerisation site of PSI, primarily a deformation of the C-terminus of PsaL and loss of chlorophyll a and β-carotene molecules.
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http://dx.doi.org/10.3389/fpls.2018.01865DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6328476PMC
January 2019

Structure and function of photosystem I in Cyanidioschyzon merolae.

Photosynth Res 2019 Mar 26;139(1-3):499-508. Epub 2018 Mar 26.

Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978, Tel Aviv, Israel.

The evolution of photosynthesis from primitive photosynthetic bacteria to higher plants has been driven by the need to adapt to a wide range of environmental conditions. The red alga Cyanidioschyzon merolae is a primitive organism, which is capable of performing photosynthesis in extreme acidic and hot environments. The study of its photosynthetic machinery may provide new insight on the evolutionary path of photosynthesis and on light harvesting and its regulation in eukaryotes. With that aim, the structural and functional properties of the PSI complex were investigated by biochemical characterization, mass spectrometry, and X-ray crystallography. PSI was purified from cells grown at 25 and 42 °C, crystallized and its crystal structure was solved at 4 Å resolution. The structure of C. merolae reveals a core complex with a crescent-shaped structure, formed by antenna proteins. In addition, the structural model shows the position of PsaO and PsaM. PsaG and PsaH are present in plant complex and are missing from the C. merolae model as expected. This paper sheds new light onto the evolution of photosynthesis, which gives a strong indication for the chimerical properties of red algae PSI. The subunit composition of the PSI core from C. merolae and its associated light-harvesting antennae suggests that it is an evolutionary and functional intermediate between cyanobacteria and plants.
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http://dx.doi.org/10.1007/s11120-018-0501-4DOI Listing
March 2019

Structure of the plant photosystem I.

Biochem Soc Trans 2018 04 27;46(2):285-294. Epub 2018 Feb 27.

Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel

Plant photosystem I (PSI) is one of the most intricate membrane complexes in nature. It comprises two complexes, a reaction center and light-harvesting complex (LHC), which together form the PSI-LHC supercomplex. The crystal structure of plant PSI was solved with two distinct crystal forms. The first, crystallized at pH 6.5, exhibited 21 symmetry; the second, crystallized at pH 8.5, exhibited 212121 symmetry. The surfaces involved in binding plastocyanin and ferredoxin are identical in both forms. The crystal structure at 2.6 Å resolution revealed 16 subunits, 45 transmembrane helices, and 232 prosthetic groups, including 143 chlorophyll , 13 chlorophyll , 27 β-carotene, 7 lutein, 2 xanthophyll, 1 zeaxanthin, 20 monogalactosyl diglyceride, 7 phosphatidyl diglyceride, 5 digalactosyl diglyceride, 2 calcium ions, 2 phylloquinone, and 3 iron sulfur clusters. The model reveals detailed interactions, providing mechanisms for excitation energy transfer and its modulation in one of nature's most efficient photochemical machine.
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http://dx.doi.org/10.1042/BST20170299DOI Listing
April 2018

Structure and function of wild-type and subunit-depleted photosystem I in Synechocystis.

Biochim Biophys Acta Bioenerg 2018 09 4;1859(9):645-654. Epub 2018 Feb 4.

Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel. Electronic address:

The ability of photosynthetic organisms to use the sun's light as a sole source of energy sustains life on our planet. Photosystems I (PSI) and II (PSII) are large, multi-subunit, pigment-protein complexes that enable photosynthesis, but this intriguing process remains to be explained fully. Currently, crystal structures of these complexes are available for thermophilic prokaryotic cyanobacteria. The mega-Dalton trimeric PSI complex from thermophilic cyanobacterium, Thermosynechococcus elongatus, was solved at 2.5 Å resolution with X-ray crystallography. That structure revealed the positions of 12 protein subunits (PsaA-F, PsaI-M, and PsaX) and 127 cofactors. Although mesophilic organisms perform most of the world's photosynthesis, no well-resolved trimeric structure of a mesophilic organism exists. Our research model for a mesophilic cyanobacterium was Synechocystis sp. PCC6803. This study aimed to obtain well-resolved crystal structures of [1] a monomeric PSI with all subunits, [2] a trimeric PSI with a reduced number of subunits, and [3] the full, trimeric wild-type PSI complex. We only partially succeeded with the first two structures, but we successfully produced the trimeric PSI structure at 2.5 Å resolution. This structure was comparable to that of the thermophilic species, but we provided more detail. The PSI trimeric supercomplex consisted of 33 protein subunits, 72 carotenoids, 285 chlorophyll a molecules, 51 lipids, 9 iron-sulfur clusters, 6 plastoquinones, 6 putative calcium ions, and over 870 water molecules. This study showed that the structure of the PSI in Synechocystis sp. PCC6803 differed from previously described PSI structures. These findings have broadened our understanding of PSI structure.
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http://dx.doi.org/10.1016/j.bbabio.2018.02.002DOI Listing
September 2018

Structure of the plant photosystem I supercomplex at 2.6 Å resolution.

Nat Plants 2017 03 1;3:17014. Epub 2017 Mar 1.

Department of Biochemistry, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.

Four elaborate membrane complexes carry out the light reaction of oxygenic photosynthesis. Photosystem I (PSI) is one of two large reaction centres responsible for converting light photons into the chemical energy needed to sustain life. In the thylakoid membranes of plants, PSI is found together with its integral light-harvesting antenna, light-harvesting complex I (LHCI), in a membrane supercomplex containing hundreds of light-harvesting pigments. Here, we report the crystal structure of plant PSI-LHCI at 2.6 Å resolution. The structure reveals the configuration of PsaK, a core subunit important for state transitions in plants, a conserved network of water molecules surrounding the electron transfer centres and an elaborate structure of lipids bridging PSI and its LHCI antenna. We discuss the implications of the structure for energy transfer and the evolution of PSI.
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http://dx.doi.org/10.1038/nplants.2017.14DOI Listing
March 2017
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