what happens in photosystem 2

Following the current working model for de novo PSII biogenesis, initial steps take place at these biogenic subcompartments and then proceeds along thylakoids until functional PSII is generated. In Salicornia europaea photosynthetic genes, PSI and PSII pigment-binding proteins, b6f complex, and ATPase synthase CF1 were significantly induced (Fan et al., 2013). Explain why these steps are bypassed; that is, why gluconeogenesis is not simply a reversal of the reactions of glycolysis. The photosynthetic light-harvesting and electron transfer system. Thus, a large cross section, long-excitation-energy lifetime, and high rate of energy transfer to the reaction center are the attributes of an efficient antenna and productive photosynthetic unit. Genes for plastidic and nuclear protein synthesis, genes with undefined functions, genes pointing to glycolysis and stress (a putative glutathione S-transferase and COBRA protein precursor) suggest the relationship of salinity with decreased photosystem II activity. An slr0151 mutant displays impaired regulation of PSII repair under high light conditions, and the Slr0151 factor interacts directly with the D1 and CP43 subunits of PSII, probably via its TPR units (Yang et al., 2014). How light energy is used to make ATP and NADPH. After the sunlight hits the surface of the leaf it goes into the plant cell. The stages from photodamage to degradation of the D1 protein are regulated by phosphorylation-dephosphorylation events of the PSII core proteins. During repair of PS II, β-carotene seems to be released from the reaction center and converted into zeaxanthin (Depka et al., 1998), so new synthesis of β-carotene is needed (Trebst and Depka, 1997). The oxidation of water to molecular oxygen requires extraction of four electrons and four protons from two molecules of water. The center of the PS II complex is a heterodimer consisting of the subunits D1 and D2 with six chl-a, two pheophytin, two plastoquinone, and one to two carotenoid molecules bound to it. Finally, high-quality crystals obtained from the purified PSII dimers are shown. The electrons present in the reaction center jumps to higher energy state on receiving light energy. Within the photosystem, enzymes capture photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce plastoquinone to plastoquinol. The two core antennae CP43 and CP47 flank both sides of the D1-D2 complex. What happens in the photosystem 2 when it is hit by a photo of light. 7). The D1 and D2 proteins are homologous to each other and also to the L proteins and M proteins from the reaction center of the purple bacteria (section 3.4). Shown are the dimeric and monomeric core complexes of PSII and PSI (gray), the antenna protein of PSI, Lhca1-4 (mixed green), and PSII, Lhcb1, Lhcb2 (pale green), Lhcb3 (dark green), Lhcb4 (blue), Lhcb5 (yellow), Lhcb6 (red). A number of compounds that are similar in their structure to plastoquinone can block the plastoquinone binding site at the D1 protein, causing inhibition of photosynthesis. Schematic presentation of a simplified structure of the photosystem II complex. Selected nuclear genes involved in high light responses, A.-V. Bohne, ... J. Nickelsen, in International Review of Cell and Molecular Biology, 2016. However they are numbered in order of how they were discovered. MET1 homologues are found in eukaryotic organisms including plants and algae, but not in prokaryotes like cyanobacteria. 7). The electrons replace the electrons that left Photosystem II and moved into the electron transport chain. Along with the PSI, it forms the electron–proton transfer chain, which drives the synthesis of adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) (Figure 1). LHCII is the main complex and contains about 40% of the PSII chlorophyll – it is the most abundant chlorophyll protein in nature. It seems that the D1 protein wears out during its function, perhaps through damage by oxygen radicals, which still occurs despite all the protection mechanisms. Figure 1. Experiments with cyanobacteria and plants have led to the identification of FtsH as the primary protease for D1 turnover, with DegP proteases possibly having a role as well (reviewed in Nixon et al., 2005). 150μ micromoles photons/m2/s) (Zhang et al., 1997). 8). Figs. Photosystem 1: Released high energy electrons are replaced by the releasing energy of photolysis. It is a metallo-oxo cluster comprising four manganese ions (in oxidation states ranging from +2 to +4)[6] and one divalent calcium ion. The excited electron is passed to the primary electron acceptor. Both are required for interaction with its cognate binding partners, the inner antenna proteins CP43 and CP47, probably during PSII assembly/reassembly (Bhuiyan et al., 2015). Detail The Source Of Electrons, Use Of Water, Generation Of O2 And NAPDH 3. PS II is located on the inner surface of the thylakoid, i.e., … After a light-induced damage to PSII, the LHCII antenna dissociates and monomerization of PSII occurs (Aro et al., 2005; Gururani et al., 2015; Yamamoto, 2016) Fig. Table 3.2. Moreover, artificial photosynthetic water-splitting may contribute to the effective use of sunlight as an alternative energy-source. In order to harvest light energy efficiently, the PSII core is surrounded by a large number of light-harvesting antenna proteins designated LHCII (light-harvesting complex II). What happens in the photosystem 2 when it is hit by a photo of light What happens in the photosystem 2 when it is hit by a photo of light Answers: 2 Get Other questions on the subject: Biology. Photosystem II (PSII) is a membrane protein supercomplex that executes the initial reaction of photosynthesis in higher plants, algae, and cyanobacteria. The inner and outer light harvesting complexes of LHC II are arranged at the periphery. Figure 8. It appears that the structure of PS II and the structure of the reaction centers in purple bacteria share the same basic features (see also Table 3.2). The two subunits CP 43 and CP 47 (CP means chlorophyll protein) each bind about 15 chlorophyll molecules and form the core complex of the antenna shown in Figure 2.10. Blocking tocopherol (vitamin E) biosynthesis by herbicide treatment of Chlamydomonas cells leads to depletion of the tocopherol pool in HL and rapid photoinactivation of PS II and net loss of D1 protein (Trebst et al., 2002), which can be prevented by simultaneous feeding of 1O2* scavengers or short-chain tocopherol analogs (Trebst et al., 2004; Kruk et al., 2005). The number of LHCII and FCPII associated with each PSII core, and their oligomerization states are different among different organisms. In Synechocystis, the reading frame slr0151 forms part of an operon and the encoded protein had previously been implicated in PSII function/activity (Wegener et al., 2008). The core of PSII consists of a pseudo-symmetric heterodimer of two homologous proteins D1 and D2. The binding of quinone to the subunits D1 and D2 is homologous to the subunits L and M in purple bacteria. The 2 e- pass through Photosystem-2 and Photosystem-1 and generate ATP molecules, like in mitochondria. Krishna K. Niyogi, in The Chlamydomonas Sourcebook, 2009. PSII in association with LHCII or FCPII are designated as PSII-LHCII and PSII-FCPII supercomplexes, respectively. [8][9][10] While obtaining these structures was in itself a great feat, they did not show the oxygen-evolving complex in full detail. Due to its complexity, the process involves an array of accessory factors. Dark phase = The Calvin Cycle – is the making of Glucose from CO2. More recently it was shown that the PratA/D1 complex defines a membrane subcompartment (the PratA-defined membrane, PDM) which can be separated from plasma and thylakoid membranes by sequential sucrose-gradient centrifugations (Schottkowski et al., 2009). Photoinhibition is accompanied by oxidative damage to D1 that necessitates repair of PS II. In principle, PratA consists of nine consecutive TPR units, and has the potential to connect multiple proteins (cf. C-terminal removal of an 8- to 16-amino acid extension is common to all photosynthetic organisms, and is required for the subsequent docking of the oxygen-evolving enhancer (OEE) proteins at the lumenal side of PSII (Diner et al., 1988; Roose and Pakrasi, 2004). A single Lhcb monomeric unit is a relatively small protein, ~25 kDa, containing three transmembrane alpha-helical structures (A, B, and C helices) and binding up to 12 molecules of chlorophyll (up to 7 chlorophyll a and 5 chlorophyll b) and up to four xanthophylls. Each photosystem consists of a light-harvesting complex and a core complex. These bind chlorophyll a, chlorophyll b, and xanthophylls to form several different complexes – LHCII (Lhcb1-3), CP29 (Lhcb4), CP26 (Lhcb5), and CP24 (Lhcb6). [1] DCMU is a chemical often used in laboratory settings to inhibit photosynthesis. Define And Discuss What Happens In Photosystem II And Photosystem I. PSII exists mainly in a dimeric form. [6] Finally, the intermediate S-states[18] were proposed by Jablonsky and Lazar as a regulatory mechanism and link between S-states and tyrosine Z. Photosystem II (PSII) is a membrane protein supercomplex that executes the initial reaction of photosynthesis in higher plants, algae, and cyanobacteria. The rate of PS II repair depends critically on the synthesis rate of new D1 protein, which is inserted cotranslationally into PS II (Adir et al., 1990). The process begins in Photosystem II, where the light harvesting complex absorbs photons and relays that energy to the reaction centre, which can refer to a specific protein within photosystem II or, more specifically, to a pair of chlorophylls within that protein. Copyright © 2021 Elsevier B.V. or its licensors or contributors. Blocking chloroplast protein synthesis with inhibitors such as chloramphenicol or lincomycin (Ohad et al., 1984) or with mutations that limit chloroplast translation (Heifetz et al., 1997) increases the rate of photoinhibition and results in net loss of D1 protein. In the prokaryotic cyanobacteria and red algae, a group of most primitive eukaryotic algae, phycobilisomes serve as light-harvesting antennas, which bind bilin pigments and are hydrophilic pigment-proteins associated at the stromal (cytoplasmic) surface of the thylakoid membranes (Adir et al., 2019). Mutant analysis revealed that PratA is involved in the C-terminal maturation of the D1 protein of the PSII reaction center (Klinkert et al., 2004). P. Horton, in Encyclopedia of Biological Chemistry (Second Edition), 2013. The Mn cluster is probably enclosed by both the D1 and D2 proteins. Homologues of FtsH and DegP are encoded in the Chlamydomonas genome (Minagawa and Takahashi, 2004). PSII monomers then migrate from the grana to the stroma-exposed thylakoid membranes where a contact with the components acting in degradation and synthesis of the D1 protein is feasible (Nishimura et al., 2016). Interestingly, MET1 in C. reinhardtii, named TEF30, seems to be involved in PSII repair and not in its de novo assembly (Michael Schroda, personal communication). Chlorophyll, which is present in the photosystems, soaks up light energy. When present, DCMU inhibits electron flow from photosystem II to plastoquinone. Photosystem II is the first step of photosynthesis, where the chlorophyll molecule uses light energy to take an electron from a water molecule. It absorbs maximum light of 700nm. The LHCII antenna forms a dynamic network, or macrodomain, of monomeric and trimeric subunits, associated with each other and the reaction-center complex. This system is responsible for the photolysis of water and involves the evolution of molecular oxygen. Based on these results, a specific role for tocopherol in scavenging 1O2* and protecting PS II from photoinhibition has been proposed (Krieger-Liszkay and Trebst, 2006). It has been estimated that the D1 protein is replaced after 106 to 107 catalytic cycles of the PS II reaction center. Chlorophyll a and b absorb light in the thylakoid mostly blue, red, and orange. Through the water-splitting reaction of PSII, light energy is converted into biologically useful chemical energy, and molecular oxygen is formed which transformed the atmosphere into an aerobic one and sustained aerobic life on the Earth. In the case of LHCII, two xanthophylls, lutein 1 and 2, are associated with the helices A and B. The subunits O, P, Q stabilize the Mn cluster. In the photosynthetic membrane, these PSII units are sometimes seen as ordered arrays, their frequency reflecting the regulation of PSII function as explained below. Start studying photosystem 1 and 2. PSII is crystallized in space group of P212121 which is SONICC active and provides positive confirmation of crystals too small to image optically, distinguishing them from amorphous precipitate or identifying them in a visibly clear drop. The water-splitting enzyme is released into the inner space. 8). PratA binds directly to an α-helical region at the D1 C-terminus which is in close proximity to Mn-complexing amino acids of the D1 protein. Each photosystem II contains at least 99 cofactors: 35 chlorophyll a, 12 beta-carotene, two pheophytin, two plastoquinone, two heme, one bicarbonate, 20 lipids, the Mn4CaO5 cluster (including two chloride ions), one non heme Fe2+ and two putative Ca2+ ions per monomer. PratA-bound Mn2+ is then transferred to D1 for the assembly of a functional Mn cluster during later steps of PSII biogenesis (Stengel et al., 2012). Both carry out the light reaction of photosynthesis. So now the race has started to solve the structure of Photosystem II at different stages in the mechanistic cycle (discussed below). What is the name of the first protein in the electron transport chain. Photoinhibition occurs when the rate of PS II inactivation and photodamage exceeds the rate of PS II repair (Ohad et al., 1984), and it is enhanced in excess light and during other abiotic stresses such as salinity stress (Neale and Melis, 1989). PratA interacts directly with an α-helical structure of 15 amino acids within the D1 C-terminus, which is located very close to the amino acids that provide coordinating residues for the Mn4CaO5 cluster (Schottkowski et al., 2009; Fig. It is likely that this interaction with D1 is mediated by the TPR domain, but this remains to be shown. Sanna Rantala, ... Eva-Mari Aro, in Reference Module in Life Sciences, 2020. Photosystem I: It has chlorophyll a molecules. The structure of the PSII core and its complex with LHC proteins has been solved by either X-ray crystallography (Ago et al., 2016; Umena et al., 2011; Shen, 2015; Suga et al., 2015) or cryo-electron microscopy (cryo-EM) (Nagao et al., 2019; Pi et al., 2019; Shen et al., 2019; Sheng et al., 2019; Su et al., 2017) from various groups of oxygenic photosynthetic organisms. Currently structures of the S1 state and the S3 state's have been published almost simultaneously from two different groups, showing the addition of an oxygen molecule designated O6 between Mn1 and Mn4,[13][14] suggesting that this may be the site on the oxygen evolving complex, where oxygen is produced. Associated tightly with the D1/D2 reaction center are the core antenna complexes CP47 and CP43. Three major parameters determine the efficiency of light harvesting: (1) the absorption cross section (or number of pigments) and their ability to intercept light quanta with the broad range of energy; (2) the time during which energy of light can be kept in antenna so it can be funneled into the reaction center; and (3) rate of the funneling. In 2011 the OEC of PSII was resolved to a level of 1.9Å revealing five oxygen atoms serving as oxo bridges linking the five metal atoms and four water molecules bound to the Mn4CaO5 cluster; more than 1,300 water molecules were found in each photosystem II monomer, some forming extensive hydrogen-bonding networks that may serve as channels for protons, water or oxygen molecules. These electrons are used in several ways. The ultrastructure of cyanobacterial PSII has recently been resolved at 1.9 Å resolution, revealing its complex organization including the architecture of the water-splitting Mn4CaO5 cluster at its lumenal side (Umena et al., 2011). Populus euphratica expression of psbA proteins, D2 protein, and Rubisco large unit were decreased after 12 h of salt shock. 1. Immunogold labeling experiments demonstrated that both PratA and the precursor of the D1 protein (pD1) localize to thylakoid membrane convergence sites at the cell periphery, which had been named thylakoid biogenesis centers (Stengel et al., 2012; Rast et al., 2015). We use cookies to help provide and enhance our service and tailor content and ads. [3] Because of this, P680+ is highly oxidizing and can take part in the splitting of water.[2]. The remainder of the antenna consists of the Lhcb proteins, Lhcb1-6. On the other hand, FCPII exists in tetrameric and monomeric forms, and two tetramers and three monomers are found to be associated with a diatom PSII core (Nagao et al., 2019; Pi et al., 2019). When sunlight is absorbed by one of many pigments present in photosystem II the light energy is distributed from pigment to pigment until it reaches the reaction center. Photosystem 2: Released high energy electrons are replaced by the electrons released from photosystem II. The process is called Phosphorylation. The LPA1 protein from A. thaliana contains near its N-terminus two TPR motifs, which are followed by two predicted transmembrane stretches located within a domain of unknown function (DUF3493) and an extended C-terminal domain (Fig. 2. This chapter describes the purification procedures leading to highly pure, homogenous, and highly active PSII core dimers from a thermophilic cyanobacterium, Thermosynechococcus vulcanus (T. vulcanus), that are used for successful crystallization and diffraction at atomic resolution. In photosystem II, the electron comes from the splitting of water, which releases oxygen as a waste product. The electrons and hydrogen ions are used to power the creation of ATP, and ultimately carbohydrates, in later stages of photosynthesis. 1. The S1 state is largely considered to consist of manganese ions with oxidation states of Mn3+, Mn3+, Mn4+, Mn4+. In a series of four charge separation events, utilizing the energy from four photons, PSII oxidizes two water molecules to obtain dioxygen, four protons, and four electrons. In photosystem I, the electron comes from the chloroplast electron transport chain. Based on this experiment, Bessel Kok and co-workers [17] introduced a cycle of five flash-induced transitions of the so-called S-states, describing the four redox states of OEC: When four oxidizing equivalents have been stored (at the S4-state), OEC returns to its basic S0-state. When it grabs electrons from a water molecule, photosystem II splits the water and releases oxygen gas. Photosystem 2: The main function of the photosystem 2 is ATP synthesis and hydrolysis of water. Details about the flow of electrons through Photosystem II, b6-f complex, Photosystem I and NADP reductase have not been included here but can be found under The Process of Photosynthesis in Plants. Biochimica et Biophysica Acta – Bioenergetics 1847, 900–909. PSII and PSI both served by light-harvesting antenna drive the oxidation of water and the reduction of NADP, connected by an electron transfer chain consisting of plastoquinone (PQ), the cytochrome bf complex (Cytbf) and plastocyanin (PC). 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