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European Journal of Biochemistry May 1996Photosystems I and II drive oxygenic photosynthesis. This requires biochemical systems with remarkable properties, allowing these membrane-bound pigment-protein... (Review)
Review
Photosystems I and II drive oxygenic photosynthesis. This requires biochemical systems with remarkable properties, allowing these membrane-bound pigment-protein complexes to oxidise water and produce NAD(P)H. The protein environment provides a scaffold in the membrane on which cofactors are placed at optimum distance and orientation, ensuring a rapid, efficient trapping and conversion of light energy. The polypeptide core also tunes the redox potentials of cofactors and provides for unidirectional progress of various reaction steps. The electron transfer pathways use a variety of inorganic and organic cofactors, including amino acids. This review sets out some of the current ideas and data on the cofactors and polypeptides of photosystems I and II.
Topics: Amino Acid Sequence; Bacterial Proteins; Electron Transport; Evolution, Molecular; Models, Molecular; Molecular Sequence Data; Oxygen; Photochemistry; Photosynthesis; Photosynthetic Reaction Center Complex Proteins; Photosystem I Protein Complex; Photosystem II Protein Complex; Plant Proteins; Protein Conformation; Sequence Homology, Amino Acid
PubMed: 8647094
DOI: 10.1111/j.1432-1033.1996.00519.x -
Frontiers in Plant Science 2023Phycobilisomes serve as a light-harvesting antenna of both photosystem I (PSI) and II (PSII) in cyanobacteria, yet direct energy transfer from phycobilisomes to PSI is...
Phycobilisomes serve as a light-harvesting antenna of both photosystem I (PSI) and II (PSII) in cyanobacteria, yet direct energy transfer from phycobilisomes to PSI is not well documented. Here we recorded picosecond time-resolved fluorescence at wavelengths of 605-760 nm in isolated photosystem I (PSI), phycobilisomes and intact cells of a PSII-deficient mutant of sp. PCC 6803 at 77 K to study excitation energy transfer and trapping. By means of a simultaneous target analysis of the kinetics of isolated complexes and whole cells, the pathways and dynamics of energy transfer and were established. We establish that the timescale of the slowest equilibration between different terminal emitters in the phycobilisome is ≈800 ps. It was estimated that the terminal emitter in about 40% of the phycobilisomes transfers its energy with a rate constant of 42 ns to PSI. This energy transfer rate is higher than the rates of equilibration within the phycobilisome - between the rods and the core or between the core cylinders - and is evidence for the existence of specific phycobilisome-PSI interactions. The rest of the phycobilisomes remain unconnected or slowly transferring energy to PSI.
PubMed: 38078099
DOI: 10.3389/fpls.2023.1293813 -
Frontiers in Plant Science 2023The need to acclimate to different environmental conditions is central to the evolution of cyanobacteria. Far-red light (FRL) photoacclimation, or FaRLiP, is an...
The need to acclimate to different environmental conditions is central to the evolution of cyanobacteria. Far-red light (FRL) photoacclimation, or FaRLiP, is an acclimation mechanism that enables certain cyanobacteria to use FRL to drive photosynthesis. During this process, a well-defined gene cluster is upregulated, resulting in changes to the photosystems that allow them to absorb FRL to perform photochemistry. Because FaRLiP is widespread, and because it exemplifies cyanobacterial adaptation mechanisms in nature, it is of interest to understand its molecular evolution. Here, we performed a phylogenetic analysis of the photosystem I subunits encoded in the FaRLiP gene cluster and analyzed the available structural data to predict ancestral characteristics of FRL-absorbing photosystem I. The analysis suggests that FRL-specific photosystem I subunits arose relatively late during the evolution of cyanobacteria when compared with some of the FRL-specific subunits of photosystem II, and that the order Nodosilineales, which include strains like and sp. PCC 7335, could have obtained FaRLiP via horizontal gene transfer. We show that the ancestral form of FRL-absorbing photosystem I contained three chlorophyll -binding sites in the PsaB2 subunit, and a rotated chlorophyll molecule in the A site of the electron transfer chain. Along with our previous study of photosystem II expressed during FaRLiP, these studies describe the molecular evolution of the photosystem complexes encoded by the FaRLiP gene cluster.
PubMed: 38053766
DOI: 10.3389/fpls.2023.1289199 -
Journal of Experimental Botany Jan 2023This article comments on: 2023. Reversible down-regulation of photosystems I and II leads to fast photosynthesis recovery after long-term drought in . Journal of...
This article comments on: 2023. Reversible down-regulation of photosystems I and II leads to fast photosynthesis recovery after long-term drought in . Journal of Experimental Botany , 336–351.
Topics: Photosystem I Protein Complex; Droughts; Photosynthesis; Light; Photosystem II Protein Complex; Light-Harvesting Protein Complexes; Zeaxanthins
PubMed: 36563105
DOI: 10.1093/jxb/erac438 -
Photosynthesis Research Sep 2012Given its unique function in light-induced water oxidation and its susceptibility to photoinactivation during photosynthesis, photosystem II (PS II) is often the focus... (Review)
Review
Given its unique function in light-induced water oxidation and its susceptibility to photoinactivation during photosynthesis, photosystem II (PS II) is often the focus of studies of photosynthetic structure and function, particularly in environmental stress conditions. Here we review four approaches for quantifying or monitoring PS II functionality or the stoichiometry of the two photosystems in leaf segments, scrutinizing the approximations in each approach. (1) Chlorophyll fluorescence parameters are convenient to derive, but the information-rich signal suffers from the localized nature of its detection in leaf tissue. (2) The gross O(2) yield per single-turnover flash in CO(2)-enriched air is a more direct measurement of the functional content, assuming that each functional PS II evolves one O(2) molecule after four flashes. However, the gross O(2) yield per single-turnover flash (multiplied by four) could over-estimate the content of functional PS II if mitochondrial respiration is lower in flash illumination than in darkness. (3) The cumulative delivery of electrons from PS II to P700(+) (oxidized primary donor in PS I) after a flash is added to steady background far-red light is a whole-tissue measurement, such that a single linear correlation with functional PS II applies to leaves of all plant species investigated so far. However, the magnitude obtained in a simple analysis (with the signal normalized to the maximum photo-oxidizable P700 signal), which should equal the ratio of PS II to PS I centers, was too small to match the independently-obtained photosystem stoichiometry. Further, an under-estimation of functional PS II content could occur if some electrons were intercepted before reaching PS I. (4) The electrochromic signal from leaf segments appears to reliably quantify the photosystem stoichiometry, either by progressively photoinactivating PS II or suppressing PS I via photo-oxidation of a known fraction of the P700 with steady far-red light. Together, these approaches have the potential for quantitatively probing PS II in vivo in leaf segments, with prospects for application of the latter two approaches in the field.
Topics: Chlorophyll; Fluorescence; Light; Oxygen; Photosystem II Protein Complex; Plant Leaves
PubMed: 22638914
DOI: 10.1007/s11120-012-9740-y -
Nature Structural & Molecular Biology Jun 2019Photochemical conversion in oxygenic photosynthesis takes place in two large protein-pigment complexes named photosystem II and photosystem I (PSII and PSI,...
Photochemical conversion in oxygenic photosynthesis takes place in two large protein-pigment complexes named photosystem II and photosystem I (PSII and PSI, respectively). Photosystems associate with antennae in vivo to increase the size of photosynthetic units to hundreds or thousands of pigments. Regulation of the interactions between antennae and photosystems allows photosynthetic organisms to adapt to their environment. In low-iron environments, cyanobacteria express IsiA, a PSI antenna, critical to their survival. Here we describe the structure of the PSI-IsiA complex isolated from the mesophilic cyanobacterium Synechocystis sp. PCC 6803. This 2-MDa photosystem-antenna supercomplex structure reveals more than 700 pigments coordinated by 51 subunits, as well as the mechanisms facilitating the self-assembly and association of IsiA with multiple PSI assemblies.
Topics: Bacterial Proteins; Cryoelectron Microscopy; Light-Harvesting Protein Complexes; Models, Molecular; Photosystem I Protein Complex; Protein Conformation; Protein Multimerization; Protein Subunits; Synechocystis
PubMed: 31133699
DOI: 10.1038/s41594-019-0228-8 -
Communications Biology May 2024Photosynthetic cryptophytes are eukaryotic algae that utilize membrane-embedded chlorophyll a/c binding proteins (CACs) and lumen-localized phycobiliproteins (PBPs) as...
Photosynthetic cryptophytes are eukaryotic algae that utilize membrane-embedded chlorophyll a/c binding proteins (CACs) and lumen-localized phycobiliproteins (PBPs) as their light-harvesting antennae. Cryptophytes go through logarithmic and stationary growth phases, and may adjust their light-harvesting capability according to their particular growth state. How cryptophytes change the type/arrangement of the photosynthetic antenna proteins to regulate their light-harvesting remains unknown. Here we solve four structures of cryptophyte photosystem I (PSI) bound with CACs that show the rearrangement of CACs at different growth phases. We identify a cryptophyte-unique protein, PsaQ, which harbors two chlorophyll molecules. PsaQ specifically binds to the lumenal region of PSI during logarithmic growth phase and may assist the association of PBPs with photosystems and energy transfer from PBPs to photosystems.
Topics: Photosystem I Protein Complex; Cryptophyta; Light-Harvesting Protein Complexes; Chlorophyll; Chlorophyll Binding Proteins; Photosynthesis; Phycobiliproteins
PubMed: 38734819
DOI: 10.1038/s42003-024-06268-5 -
Bioresource Technology Feb 2019This study investigated the interrelations between hydrogen synthesis and Photosystem I electron transport rate in Chlamydomonas reinhardtii. The fluorescence of both...
This study investigated the interrelations between hydrogen synthesis and Photosystem I electron transport rate in Chlamydomonas reinhardtii. The fluorescence of both photosystems (PS I and PS II) was monitored using a Dual Pulse Amplitude Modulated (PAM) Fluorometer. Hydrogen synthesis was induced by eliminating sulphur from the growth media (TAP-S). Multiple physiological parameters [rETR, Y (I), Y (II), NPQ, α, F/F and YI:YII] were recorded using the Dual PAM and correlated to hydrogen produced. There was a 66% increase in Photosystem I rETR during hydrogen production. A significant direct correlation existed between PS 1 rETR and hydrogen evolution values over the ten-day period (r = 0.895, p < 0.01) indicating that PS I can be considered as a driver of H production. Significant correlations between rETR of PS I and H evolution suggest a novel physiological indicator to monitor H production during the three critical phases identified in this study.
Topics: Chlamydomonas reinhardtii; Electron Transport; Fluorescence; Hydrogen; Photosynthesis; Photosystem I Protein Complex; Sulfur
PubMed: 30448683
DOI: 10.1016/j.biortech.2018.10.019 -
Plant Science : An International... Feb 2021Under natural field conditions, plants usually experience fluctuating light (FL) under moderate heat stress in summer. However, responses of photosystems I and II (PSI...
Under natural field conditions, plants usually experience fluctuating light (FL) under moderate heat stress in summer. However, responses of photosystems I and II (PSI and PSII) to such combined stresses are not well known. Furthermore, the role of water-water cycle (WWC) in photoprotection in FL under moderate heat stress is poorly understood. In this study, we examined chlorophyll fluorescence and P700 redox state in FL at 42 °C in two orchids, Dendrobium officinale (with high WWC activity) and Bletilla striata (with low WWC activity). After FL treatment at 42 °C, PSI activity maintained stable while PSII activity decreased significantly in these two orchids. In D. officinale, the WWC could rapidly consume the excess excitation energy in PSI and thus avoided an over-reduction of PSI upon any increase in illumination. Therefore, in D. officinale, WWC likely protected PSI in FL at 42 °C. In B. striata, heat-induced PSII photoinhibition down-regulated electron flow from PSII and thus prevented an over-reduction of PSI after transition from low to high light. Consequently, in B. striata moderate PSII photoinhibition could protected PSI in FL at 42 °C. We conclude that, in addition to cyclic electron flow, WWC and PSII photoinhibition-repair cycle are two important strategies for preventing PSI photoinhibition in FL under moderate heat stress.
Topics: Dendrobium; Heat-Shock Response; Light; Orchidaceae; Oxidation-Reduction; Photosystem I Protein Complex; Photosystem II Protein Complex
PubMed: 33487367
DOI: 10.1016/j.plantsci.2020.110795 -
Current Opinion in Structural Biology Apr 2002The recently determined crystal structures of photosystems I and II at 2.5 A and 3.8 A resolution, respectively, have improved the structural basis for understanding the... (Review)
Review
The recently determined crystal structures of photosystems I and II at 2.5 A and 3.8 A resolution, respectively, have improved the structural basis for understanding the processes of light trapping, exciton transfer and electron transfer occurring in the primary steps of oxygenic photosynthesis. Understanding the assembly of the 12 protein subunits and 128 cofactors in photosystem I allows us to study the possible functions of the individual players in this protein-cofactor complex.
Topics: Carotenoids; Chlorophyll; Chlorophyll A; Cyanobacteria; Electron Transport; Light-Harvesting Protein Complexes; Lipid Metabolism; Lipids; Models, Molecular; Photosynthetic Reaction Center Complex Proteins; Photosystem I Protein Complex; Protein Conformation; Protein Subunits
PubMed: 11959504
DOI: 10.1016/s0959-440x(02)00317-2