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1
Levin, Guy, et Gadi Schuster. « LHC-like Proteins : The Guardians of Photosynthesis ». International Journal of Molecular Sciences 24, no 3 (28 janvier 2023) : 2503. http://dx.doi.org/10.3390/ijms24032503.
Texte intégralRésumé :
The emergence of chlorophyll-containing light-harvesting complexes (LHCs) was a crucial milestone in the evolution of photosynthetic eukaryotic organisms. Light-harvesting chlorophyll-binding proteins form complexes in proximity to the reaction centres of photosystems I and II and serve as an antenna, funnelling the harvested light energy towards the reaction centres, facilitating photochemical quenching, thereby optimizing photosynthesis. It is now generally accepted that the LHC proteins evolved from LHC-like proteins, a diverse family of proteins containing up to four transmembrane helices. Interestingly, LHC-like proteins do not participate in light harvesting to elevate photosynthesis activity under low light. Instead, they protect the photosystems by dissipating excess energy and taking part in non-photochemical quenching processes. Although there is evidence that LHC-like proteins are crucial factors of photoprotection, the roles of only a few of them, mainly the stress-related psbS and lhcSR, are well described. Here, we summarize the knowledge gained regarding the evolution and function of the various LHC-like proteins, with emphasis on those strongly related to photoprotection. We further suggest LHC-like proteins as candidates for improving photosynthesis in significant food crops and discuss future directions in their research.
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Rochaix, Jean-David, et Roberto Bassi. « LHC-like proteins involved in stress responses and biogenesis/repair of the photosynthetic apparatus ». Biochemical Journal 476, no 3 (14 février 2019) : 581–93. http://dx.doi.org/10.1042/bcj20180718.
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AbstractLHC (light-harvesting complex) proteins of plants and algae are known to be involved both in collecting light energy for driving the primary photochemical reactions of photosynthesis and in photoprotection when the absorbed light energy exceeds the capacity of the photosynthetic apparatus. These proteins usually contain three transmembrane (TM) helices which span the thylakoid membranes and bind several chlorophyll, carotenoid and lipid molecules. In addition, the LHC protein family includes LHC-like proteins containing one, two, three or even four TM domains. One-helix proteins are not only present in eukaryotic photosynthetic organisms but also in cyanobacteria where they have been named high light-inducible proteins. These small proteins are probably the ancestors of the members of the extant LHC protein family which arouse through gene duplications, deletions and fusions. During evolution, some of these proteins have diverged and acquired novel functions. In most cases, LHC-like proteins are induced in response to various stress conditions including high light, high salinity, elevated temperature and nutrient limitation. Many of these proteins play key roles in photoprotection, notably in non-photochemical quenching of absorbed light energy. Moreover, some of these proteins appear to be involved in the regulation of chlorophyll synthesis and in the assembly and repair of Photosystem II and also of Photosystem I possibly by mediating the insertion of newly synthesized pigments into the photosynthetic reaction centers.
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Rathod, Mithun Kumar, Sreedhar Nellaepalli, Shin-Ichiro Ozawa, Hiroshi Kuroda, Natsumi Kodama, Sandrine Bujaldon, Francis-André Wollman et Yuichiro Takahashi. « Assembly Apparatus of Light-Harvesting Complexes : Identification of Alb3.1–cpSRP–LHCP Complexes in the Green Alga Chlamydomonas reinhardtii ». Plant and Cell Physiology 63, no 1 (1 octobre 2021) : 70–81. http://dx.doi.org/10.1093/pcp/pcab146.
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Abstract The unicellular green alga, Chlamydomonas reinhardtii, contains many light-harvesting complexes (LHCs) associating chlorophylls a/b and carotenoids; the major LHCIIs (types I, II, III and IV) and minor light-harvesting complexes, CP26 and CP29, for photosystem II, as well as nine LHCIs (LHCA1–9), for photosystem I. A pale green mutant BF4 exhibited impaired accumulation of LHCs due to deficiency in the Alb3.1 gene, which encodes the insertase involved in insertion, folding and assembly of LHC proteins in the thylakoid membranes. To elucidate the molecular mechanism by which ALB3.1 assists LHC assembly, we complemented BF4 to express ALB3.1 fused with no, single or triple Human influenza hemagglutinin (HA) tag at its C-terminus (cAlb3.1, cAlb3.1-HA or cAlb3.1–3HA). The resulting complemented strains accumulated most LHC proteins comparable to wild-type (WT) levels. The affinity purification of Alb3.1-HA and Alb3.1–3HA preparations showed that ALB3.1 interacts with cpSRP43 and cpSRP54 proteins of the chloroplast signal recognition particle (cpSRP) and several LHC proteins; two major LHCII proteins (types I and III), two minor LHCII proteins (CP26 and CP29) and eight LHCI proteins (LHCA1, 2, 3, 4, 5, 6, 8 and 9). Pulse-chase labeling experiments revealed that the newly synthesized major LHCII proteins were transiently bound to the Alb3.1 complex. We propose that Alb3.1 interacts with cpSRP43 and cpSRP54 to form an assembly apparatus for most LHCs in the thylakoid membranes. Interestingly, photosystem I (PSI) proteins were also detected in the Alb3.1 preparations, suggesting that the integration of LHCIs to a PSI core complex to form a PSI–LHCI subcomplex occurs before assembled LHCIs dissociate from the Alb3.1–cpSRP complex.
4
Brunner, Harald, et Wolfhart Rüdiger. « On the Expression of Several Lhc Genes in Garden Cress (Lepidium sativum L.) ». Zeitschrift für Naturforschung C 49, no 11-12 (1 décembre 1994) : 802–10. http://dx.doi.org/10.1515/znc-1994-11-1216.
Texte intégralRésumé :
The polymerase chain reaction was used to prepare gene-specific probes for several Lhc genes coding for chlorophyll a/b-binding proteins of cress (Lepidium sativum L.). Due to the presence of about 150 basepairs of the coding region, the isolated clones could be attributed to Lhc a3 (1 clone), Lhc b1 (5 clones), Lhc b2 (1 clone) and Lhc b3 (1 clone) genes. Probes prepared from the 3′ non-coding regions of the clones did not cross-hybridize; they were specific for 3 different Lhc b1 transcripts and one each of Lhc b2, Lhc b3 and Lhc a 3 transcripts. The transcript levels were higher in leaves than in cotyledons of light-grown seedlings; they decreased significantly in cotyledons from week 1 to week 4. The levels of 2 Lhc b1 transcripts (detected with probes cd 1 and cd 2) changed from 1 week old cotyledons (30% c d l, 28% cd 2) to 3 months old leaves (14% c d l), 44% cd 2), stems (11% c d l, 56% cd 2) and fruits (15% cd 1, 62% cd 2, all values percent of total transcripts), whereas transcript levels of another Lhc b1 gene (detected with probe cd 3) and of a Lhc a 3 gene remained nearly constant. The level of Lhc b2 and Lhc b3 transcripts were 1 - 2 orders of magnitude smaller than those of the other Lhc transcripts. The data obtained with cress plants are compared with published data from other plants.
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Lan, Yanhong, Yao Song, Fei Zhao, Yu Cao, Dening Luo, Dairong Qiao, Yi Cao et Hui Xu. « Phylogenetic, Structural and Functional Evolution of the LHC Gene Family in Plant Species ». International Journal of Molecular Sciences 24, no 1 (28 décembre 2022) : 488. http://dx.doi.org/10.3390/ijms24010488.
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Light-harvesting chlorophyll a/b-binding (LHC) superfamily proteins play a vital role in photosynthesis. Although the physiological and biochemical functions of LHC genes have been well-characterized, the structural evolution and functional differentiation of the products need to be further studied. In this paper, we report the genome-wide identification and phylogenetic analysis of LHC genes in photosynthetic organisms. A total of 1222 non-redundant members of the LHC family were identified from 42 species. According to the phylogenetic clustering of their homologues with Arabidopsis thaliana, they can be divided into four subfamilies. In the subsequent evolution of land plants, a whole-genome replication (WGD) event was the driving force for the evolution and expansion of the LHC superfamily, with its copy numbers rapidly increasing in angiosperms. The selection pressure of photosystem II sub-unit S (PsbS) and ferrochelatase (FCII) families were higher than other subfamilies. In addition, the transcriptional expression profiles of LHC gene family members in different tissues and their expression patterns under exogenous abiotic stress conditions significantly differed, and the LHC genes are highly expressed in mature leaves, which is consistent with the conclusion that LHC is mainly involved in the capture and transmission of light energy in photosynthesis. According to the expression pattern and copy number of LHC genes in land plants, we propose different evolutionary trajectories in this gene family. This study provides a basis for understanding the molecular evolutionary characteristics and evolution patterns of plant LHCs.
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Darr, S. C., S. C. Somerville et C. J. Arntzen. « Monoclonal antibodies to the light-harvesting chlorophyll a/b protein complex of photosystem II. » Journal of Cell Biology 103, no 3 (1 septembre 1986) : 733–40. http://dx.doi.org/10.1083/jcb.103.3.733.
Texte intégralRésumé :
A collection of 17 monoclonal antibodies elicited against the light-harvesting chlorophyll a/b protein complex which serves photosystem II (LHC-II) of Pisum sativum shows six classes of binding specificity. Antibodies of two of the classes recognize a single polypeptide (the 28- or the 26- kD polypeptides), thereby suggesting that the two proteins are not derived from a common precursor. Other classes of antibodies cross-react with several polypeptides of LHC-II or with polypeptides of both LHC-II and the light-harvesting chlorophyll a/b polypeptides of photosystem I (LHC-I), indicating that there are structural similarities among the polypeptides of LHC-II and LHC-I. The evidence for protein processing by which the 26-, 25.5-, and 24.5-kD polypeptides are derived from a common precursor polypeptide is discussed. Binding studies using antibodies specific for individual LHC-II polypeptides were used to quantify the number of antigenic polypeptides in the thylakoid membrane. 27 copies of the 26-kD polypeptide and two copies of the 28-kD polypeptide were found per 400 chlorophylls. In the chlorina f2 mutant of barley, and in intermittent light-treated barley seedlings, the amount of the 26-kD polypeptide in the thylakoid membranes was greatly reduced, while the amount of 28-kD polypeptide was apparently not affected. We propose that stable insertion and assembly of the 28-kD polypeptide, unlike the 26-kD polypeptide, is not regulated by the presence of chlorophyll b.
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Droppa, Magdolna, Jiri Masojidek et Gábor Horváth. « Changes of the Polypeptide Composition in Thylakoid Membranes during Differentiation ». Zeitschrift für Naturforschung C 45, no 3-4 (1 avril 1990) : 253–57. http://dx.doi.org/10.1515/znc-1990-3-419.
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Changes in membrane polypeptide composition during greening of etiolated maize were investigated to confirm the existence of the developmental polypeptides of 12 - 15 kDa described recently in virescent soybean mutant [M. Droppa, M. L. Ghirardi, G. Horváth, and A. Melis, Biochim. Biophys. Acta 932, 138 - 145 (1988)]. These low molecular weight polypeptides were the most abundant proteins at the early stage of greening, but were largely absent from fully developed thylakoids. During greening the relative concentration of the 12-15 kDa polypeptides were inversely proportional to that of LHC II, suggesting a role of these polypeptides in the assembly of the LHC II and/or chloroplast development.
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Ke, Shanqiang, Chiwon W. Lee et Murray E. Duysen. « Influence of the rolC Gene on Proteins Associated with Stroma and Thylakoid Membranes of Chloroplasts in Transgenic Plants of Kentucky Bluegrass ». HortScience 32, no 3 (juin 1997) : 482D—482. http://dx.doi.org/10.21273/hortsci.32.3.482d.
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The effects of the expression of the rolC gene on protein accumulation in the chloroplasts of transgenic Kentucky bluegrass (Poa pratensis L.) were investigated. Coleoptile tissues excised from 3-day dark-grown seedlings were bombarded with tungsten particles coated with DNA of the engineered plasmid, pGA-GUSGF, containing the npt II, gus, and rolC genes. The tissues were cultured on callus induction medium, which consists of MS salts supplemented with 0.2 mg/L picloram, 0.01 mg/L naphthaleneacetic acid (NAA) 250 mg/L kanamycin, and 100 mM acetosyringone. The putative transformants were either albinos or variegated plants composed of white and green sections. These albino plants had little or no stroma-based 56-kDa and 14-kDa subunits of the suspected Rubisco proteins, which are expressed in response to genes in the nucleus and plastid, respectively. The albino plants also lacked the 110-kDa and 57–58-kDa, and 43, 47-kDa polypeptides in PS I, coupling factor, and PS II in thylakoid membranes, respectively. These proteins involved in photosynthesis are translated from plastidbased genes. No light-harvesting complex proteins (LHC) were observed in these albino plants. LHC genes are encoded in the nucleus. The thylakoid membrane proteins in the chloroplasts of the rolC transgenic variegated plants contained these proteins. Our data suggest that the nucleus and plastid gene products for plastid development are concomitantly impaired by expression of genes in the transgenic plants.
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Evans, JR. « Acclimation by the Thylakoid Membranes to Growth Irradiance and the Partitioning of Nitrogen Between Soluble and Thylakoid Proteins ». Functional Plant Biology 15, no 2 (1988) : 93. http://dx.doi.org/10.1071/pp9880093.
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Three characteristics of shade plants are reviewed. Firstly, they have relatively more chlorophyll b and the associated light-harvesting chlorophyll a/b-protein complex (LHC). Two currently accepted reasons for this are not supported by quantitative analysis. Instead, the reduced protein cost of complexing chlorophyll in LHC and the turnover of the 32 kDa herbicide binding protein are considered. Secondly, shade plants have low electron transport capacities per unit of chlorophyll. This is primarily related to a reduction in the amount of electron transport components such as the cytochrome f complex and the ATPase. The nitrogen cost of the thylakoid membranes per unit of light absorbed is thereby reduced, but the irradiance range over which light is used with high efficiency is also reduced. Thirdly, shade plants have less RuP2 carboxylase and other soluble proteins for a given amount of chlorophyll. However, while the ratio of RuP2 carboxylase protein to thylakoid protein declined, the ratio of the RuP2 carboxylase activity to electron transport activity increased. For several species, the relationship between the rate of CO2 assimilation and leaf nitrogen content depends on the irradiance during growth.
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Wu, Guangxi, Lin Ma, Cai Yuan, Jiahao Dai, Lai Luo, Roshan Sharma Poudyal, Richard T. Sayre et Choon-Hwan Lee. « Formation of light-harvesting complex II aggregates from LHCII–PSI–LHCI complexes in rice plants under high light ». Journal of Experimental Botany 72, no 13 (3 mai 2021) : 4938–48. http://dx.doi.org/10.1093/jxb/erab188.
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Abstract During low light- (LL) induced state transitions in dark-adapted rice (Oryza sativa) leaves, light-harvesting complex (LHC) II become phosphorylated and associate with PSI complexes to form LHCII–PSI–LHCI supercomplexes. When the leaves are subsequently transferred to high light (HL) conditions, phosphorylated LHCII complexes are no longer phosphorylated. Under the HL-induced transition in LHC phosphorylation status, we observed a new green band in the stacking gel of native green–PAGE, which was determined to be LHCII aggregates by immunoblotting and 77K chlorophyll fluorescence analysis. Knockout mutants of protein phosphatase 1 (PPH1) which dephosphorylates LHCII failed to form these LHCII aggregates. In addition, the ability to develop non-photochemical quenching in the PPH1 mutant under HL was less than for wild-type plants. As determined by immunoblotting analysis, LHCII proteins present in LHCII–PSI–LHCI supercomplexes included the Lhcb1 and Lhcb2 proteins. In this study, we provide evidence suggesting that LHCII in the LHCII–PSI–LHCI supercomplexes are dephosphorylated and subsequently form aggregates to dissipate excess light energy under HL conditions. We propose that this LHCII aggregation, involving LHCII L-trimers, is a newly observed photoprotective light-quenching process operating in the early stage of acclimation to HL in rice plants.
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Takeuchi, TS, et JP Thornber. « Heat-Induced Alterations in Thylakoid Membrane Protein Composition in Barley ». Functional Plant Biology 21, no 6 (1994) : 759. http://dx.doi.org/10.1071/pp9940759.
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Biochemical and spectroscopic studies on the effects of high temperatures (45-47� C) over a 1 h period on the protein composition, fluorescence and photochemical activities of the barley thylakoid membrane were made. Photosystem II (PS II) activity decreased as expected, and photosystem I (PS I) activity also unexpectedly decreased. Our data support previous conclusions that the decrease in PS I activity is largely due to inactivation (or loss) of a component between the two photosystems. A two-dimensional electrophoretic system permitted first the separation of the thylakoid pigment-protein complexes of unstressed and stressed plants, followed by a determination of their subunit composition. The changes in the protein composition of each pigment-protein complex in response to elevated temperatures were monitored. Heat changed the quaternary structure of PS II and resulted in removal of the oxygen-evolving enhancer proteins from the thylakoid, but did essentially no damage to the PS I complex. The PS II core complex dissociated from a dimeric form to a monomeric one, and the major LHC II component (LHC IIb) changed from a trimeric to a monomeric form. The pigments that are lost from thylakoids during heat stress are mainly removed from the PS II pigment-proteins.
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Calvaruso, Claudio, Anne Rokka, Eva-Mari Aro et Claudia Büchel. « Specific Lhc Proteins Are Bound to PSI or PSII Supercomplexes in the Diatom Thalassiosira pseudonana ». Plant Physiology 183, no 1 (20 mars 2020) : 67–79. http://dx.doi.org/10.1104/pp.20.00042.
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Krawczyk, Stanisz xl;law, Zbigniew Krupa et Waldemar Maksymiec. « Stark spectra of chlorophylls and carotenoids in antenna pigment-proteins LHC-II and CP-II ». Biochimica et Biophysica Acta (BBA) - Bioenergetics 1143, no 3 (juillet 1993) : 273–81. http://dx.doi.org/10.1016/0005-2728(93)90198-o.
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Funk, Christiane, Meriem Alami, Tania Tibiletti et Beverley R. Green. « High light stress and the one-helix LHC-like proteins of the cryptophyte Guillardia theta ». Biochimica et Biophysica Acta (BBA) - Bioenergetics 1807, no 7 (juillet 2011) : 841–46. http://dx.doi.org/10.1016/j.bbabio.2011.03.011.
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Kuryanchyk, T. G., et N. V. Kozel. « GENE EXPRESSION AND THE CONTENT OF STRUCTURAL PROTEINS ; OF PHOTOSYSTEMS IN BARLEY LEAVES UNDER SOIL DROUGHT ». Молекулярная и прикладная генетика 33 (12 novembre 2022) : 38–46. http://dx.doi.org/10.47612/1999-9127-2022-33-38-46.
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A significant effect of soil drought on the gene expression (psaA, psaB, lhca2, psbA, lhcb1 and lhcb4) encoding key structural proteins of reaction centers (RC) and light harvesting complexes (LHC) of photosystems (PS) in barley leaves was shown. A change in the level of gene expression observed under drought conditions is light-dependent — in normal light, there is a significant increase in the expression of lhcb1 (1.6 times), psaA (1.8 times) and psaB (2.5 times) genes, encoding PS I and II proteins, and in the dim light, on the contrary, there is a decrease in the expression of genes encoding the proteins PS II (psbA, lhcb1 and lhcb4) and protein A (psaA) of the PS I RC. It was found that under drought conditions the expression of the gene SOD3 encoding the chloroplast isoform of the antioxidant superoxide
dismutase (SOD) enzyme Fe-SOD increases multiple times. The data obtained indicate the induction of oxidative stress by drought in the chloroplasts of the leaves of barley plants.
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ROKKA, Anne, Marjaana SUORSA, Ammar SALEEM, Natalia BATTCHIKOVA et Eva-Mari ARO. « Synthesis and assembly of thylakoid protein complexes : multiple assembly steps of photosystem II ». Biochemical Journal 388, no 1 (10 mai 2005) : 159–68. http://dx.doi.org/10.1042/bj20042098.
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To study the synthesis and assembly of multisubunit thylakoid protein complexes, we performed [35S]Met pulse and chase experiments with isolated chloroplasts and intact leaves of spinach (Spinacia oleracea L.), followed by Blue Native gel separation of the (sub)complexes and subsequent identification of the newly synthesized and assembled protein subunits. PSII (photosystem II) core subunits were the most intensively synthesized proteins, particularly in vitro and at high light intensities in vivo, and could be sequestered in several distinct PSII subassemblies. Newly synthesized D1 was first found in the reaction centre complex that also contained labelled D2 and two labelled low-molecular-mass proteins. The next biggest PSII subassembly contained CP47 also. Then PsbH was assembled together with at least two other labelled chloroplast-encoded low-molecular-mass subunits, PsbM and PsbTc, and a nuclear-encoded PsbR. Subsequently, CP43 was inserted into the PSII complex concomitantly with PsbK. These assembly steps seemed to be essential for the dimerization of PSII core monomers. Intact PSII core monomer was the smallest subcomplex harbouring the newly synthesized 33 kDa oxygen-evolving complex protein PsbO. Nuclear-encoded PsbW was synthesized only at low light intensities concomitantly with Lhcb polypeptides and was distinctively present in PSII–LHCII (where LHC stands for light-harvesting complex) supercomplexes. The PsbH protein, on the contrary, was vigorously synthesized and incorporated into PSII core monomers together with the D1 protein, suggesting an intrinsic role for PsbH in the photoinhibition-repair cycle of PSII.
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Zhao, Yongguo, Hua Kong, Yunling Guo et Zhi Zou. « Light-harvesting chlorophyll a/b-binding protein-coding genes in jatropha and the comparison with castor, cassava and arabidopsis ». PeerJ 8 (28 janvier 2020) : e8465. http://dx.doi.org/10.7717/peerj.8465.
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The Lhc (light-harvesting chlorophyll a/b-binding protein) superfamily represents a class of antennae proteins that play indispensable roles in capture of solar energy as well as photoprotection under stress conditions. Despite their importance, little information has been available beyond model plants. In this study, we presents a first genome-wide analysis of Lhc superfamily genes in jatropha (Jatropha curcas L., Euphorbiaceae), an oil-bearing plant for biodiesel purpose. A total of 27 members were identified from the jatropha genome, which were shown to distribute over nine out of the 11 chromosomes. The superfamily number is comparable to 28 present in castor (Ricinus communis, Euphorbiaceae), but relatively less than 35 in cassava (Manihot esculenta, Euphorbiaceae) and 34 in arabidopsis (Arabidopsis thaliana) that experienced one or two recent whole-genome duplications (WGDs), respectively. In contrast to a high number of paralogs present in cassava and arabidopsis, few duplicates were found in jatropha as observed in castor, corresponding to no recent WGD occurred in these two species. Nevertheless, 26 orthologous groups representing four defined families were found in jatropha, and nearly one-to-one orthologous relationship was observed between jatropha and castor. By contrast, a novel group named SEP6 was shown to have been lost in arabidopsis. Global transcriptome profiling revealed a predominant expression pattern of most JcLhc superfamily genes in green tissues, reflecting their key roles in photosynthesis. Moreover, their expression profiles upon hormones, drought, and salt stresses were also investigated. These findings not only improve our knowledge on species-specific evolution of the Lhc supergene family, but also provide valuable information for further studies in jatropha.
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Allorent, Guillaume, Linnka Lefebvre-Legendre, Richard Chappuis, Marcel Kuntz, Thuy B. Truong, Krishna K. Niyogi, Roman Ulm et Michel Goldschmidt-Clermont. « UV-B photoreceptor-mediated protection of the photosynthetic machinery inChlamydomonas reinhardtii ». Proceedings of the National Academy of Sciences 113, no 51 (5 décembre 2016) : 14864–69. http://dx.doi.org/10.1073/pnas.1607695114.
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Life on earth is dependent on the photosynthetic conversion of light energy into chemical energy. However, absorption of excess sunlight can damage the photosynthetic machinery and limit photosynthetic activity, thereby affecting growth and productivity. Photosynthetic light harvesting can be down-regulated by nonphotochemical quenching (NPQ). A major component of NPQ is qE (energy-dependent nonphotochemical quenching), which allows dissipation of light energy as heat. Photodamage peaks in the UV-B part of the spectrum, but whether and how UV-B induces qE are unknown. Plants are responsive to UV-B via the UVR8 photoreceptor. Here, we report in the green algaChlamydomonas reinhardtiithat UVR8 induces accumulation of specific members of the light-harvesting complex (LHC) superfamily that contribute to qE, in particular LHC Stress-Related 1 (LHCSR1) and Photosystem II Subunit S (PSBS). The capacity for qE is strongly induced by UV-B, although the patterns of qE-related proteins accumulating in response to UV-B or to high light are clearly different. The competence for qE induced by acclimation to UV-B markedly contributes to photoprotection upon subsequent exposure to high light. Our study reveals an anterograde link between photoreceptor-mediated signaling in the nucleocytosolic compartment and the photoprotective regulation of photosynthetic activity in the chloroplast.
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Violin, Kalan Bastos, Christiane Ribeiro, Tamiye Simone Goia, José Carlos Bressiani et Ana Helena de Almeida Bressiani. « Lectinhistochemistry Evaluation of Rabbits Tibia Implanted with Macroporous Biphasic Ceramic Implants ». Key Engineering Materials 529-530 (novembre 2012) : 331–36. http://dx.doi.org/10.4028/www.scientific.net/kem.529-530.331.
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Many techniques are used to assess biomaterials implants, always intending to measure osseointegration success and tissue response facing the implanted material. Calcium phosphates are widely used as biomaterial and a major component of bone. Many processing methods have been used to achieve porous materials to allow bone ingrowth with an osteoconductive scaffold for bone. To obtain the macroporous BCP implant it was processed by direct consolidation using the protein-action technique, a globular protein based consolidation with ovalbumin. The samples were sintered at 1250°C for 30 minutes, after sintering samples were cut in 4mm diameter cylinders, with 73% volume of porosity and mean pore size ranging about 100 µm. In the present work the macroporous BCP of HAp:β-TCP is assessed after bone implantation in rabbits tibia by lectinhistochemistry (LHC) technique. Lectins are proteins from non-imune origin which binds with strong specificity carbohydrates, LHC is a technique which mark histologically carbohydrates present in glycoproteins of cells. The macroporous BCP cylindrical samples were implanted in male rabbits tibia to the evaluation of biocompatibility and osseointegration in a period of 2 weeks to 4 weeks. After euthanasia of rabbits, tibia samples from the surgery site were taken and fixed with formalin, decalcified, dehydrated and embedded with paraffin to perform histological slides for both morphological and molecular evaluation. The morphological evaluation were performed on histological slides stained with Haematoxilin and Eosin (HE), while for molecular evaluation LHC was performed on histological slides using the lectins PNA, UEA-1, WGA, sWGA and RCA-1 (Vector Labs). All samples osseointegrated well with the bone and the neoformed bone surrounding the implant took the shape of its surface. The implants also allowed bone ingrowth inside the pores towards the center of implant, characterized by islets of round bone present in the HE stained slides.
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Proctor, Matthew S., Marek Pazderník, Philip J. Jackson, Jan Pilný, Elizabeth C. Martin, Mark J. Dickman, Daniel P. Canniffe et al. « Xanthophyll carotenoids stabilise the association of cyanobacterial chlorophyll synthase with the LHC-like protein HliD ». Biochemical Journal 477, no 20 (29 octobre 2020) : 4021–36. http://dx.doi.org/10.1042/bcj20200561.
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Chlorophyll synthase (ChlG) catalyses a terminal reaction in the chlorophyll biosynthesis pathway, attachment of phytol or geranylgeraniol to the C17 propionate of chlorophyllide. Cyanobacterial ChlG forms a stable complex with high light-inducible protein D (HliD), a small single-helix protein homologous to the third transmembrane helix of plant light-harvesting complexes (LHCs). The ChlG–HliD assembly binds chlorophyll, β-carotene, zeaxanthin and myxoxanthophyll and associates with the YidC insertase, most likely to facilitate incorporation of chlorophyll into translated photosystem apoproteins. HliD independently coordinates chlorophyll and β-carotene but the role of the xanthophylls, which appear to be exclusive to the core ChlG–HliD assembly, is unclear. Here we generated mutants of Synechocystis sp. PCC 6803 lacking specific combinations of carotenoids or HliD in a background with FLAG- or His-tagged ChlG. Immunoprecipitation experiments and analysis of isolated membranes demonstrate that the absence of zeaxanthin and myxoxanthophyll significantly weakens the interaction between HliD and ChlG. ChlG alone does not bind carotenoids and accumulation of the chlorophyllide substrate in the absence of xanthophylls indicates that activity/stability of the ‘naked’ enzyme is perturbed. In contrast, the interaction of HliD with a second partner, the photosystem II assembly factor Ycf39, is preserved in the absence of xanthophylls. We propose that xanthophylls are required for the stable association of ChlG and HliD, acting as a ‘molecular glue’ at the lateral transmembrane interface between these proteins; roles for zeaxanthin and myxoxanthophyll in ChlG–HliD complexation are discussed, as well as the possible presence of similar complexes between LHC-like proteins and chlorophyll biosynthesis enzymes in plants.
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Kohorn, B. D., E. Harel, P. R. Chitnis, J. P. Thornber et E. M. Tobin. « Functional and mutational analysis of the light-harvesting chlorophyll a/b protein of thylakoid membranes. » Journal of Cell Biology 102, no 3 (1 mars 1986) : 972–81. http://dx.doi.org/10.1083/jcb.102.3.972.
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The precursor for a Lemna light-harvesting chlorophyll a/b protein (pLHCP) has been synthesized in vitro from a single member of the nuclear LHCP multigene family. We report the sequence of this gene. When incubated with Lemna chloroplasts, the pLHCP is imported and processed into several polypeptides, and the mature form is assembled into the light-harvesting complex of photosystem II (LHC II). The accumulation of the processed LHCP is enhanced by the addition to the chloroplasts of a precursor and a co-factor for chlorophyll biosynthesis. Using a model for the arrangement of the mature polypeptide in the thylakoid membrane as a guide, we have created mutations that lie within the mature coding region. We have studied the processing, the integration into thylakoid membranes, and the assembly into light-harvesting complexes of six of these deletions. Four different mutant LHCPs are found as processed proteins in the thylakoid membrane, but only one appears to have an orientation in the membrane that is similar to that of the wild type. No mutant LHCP appears in LHC II. The other two mutant LHCPs cannot be detected within the chloroplasts. We conclude that stable complex formation is not required for the processing and insertion of altered LHCPs into the thylakoid membrane. We discuss the results in light of our model.
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Szigeti, Zoltán, Éva Sárvári et Endre Lehoczki. « Chlorophyll Proteins and Lipids in Paraquat Treated Sensitive and Resistant Conyza Canadensis Leaves ». Zeitschrift für Naturforschung C 47, no 5-6 (1 juin 1992) : 400–405. http://dx.doi.org/10.1515/znc-1992-0614.
Texte intégralRésumé :
Photosynthetic activity and molecular composition of thylakoid membranes of sensitive and atrazine/paraquat coresistant biotypes of Conyza canadensis (L.) Cronq was compared before and after 5 × 10-4 molar paraquat spraying. In contrast to the irreversibly damaged sensitive plants the Rfd values (vitality indices) calculated from parameters of fluorescence induction curves, and the in vivo CO2 fixation in resistant plants showed - after a transitory inhibition - a recovery. Resistant thylakoids contained higher amount of PS II and LHC II, (i.e. lower relative amount of CP I) which can be the result of an adaptation process. Fatty acid composition of total leaf extract was almost the same in both biotype even after spraying. The amount of the oligomeric form of LHCP II decreased in paraquat treated sensitive thylakoids, which was in correlation with the reduction of Δ3-transhexadecanoic acid content. Decrease in oligomeric LHCP II and/or special lipids (PG) in sensitive thylakoids may change the association of LHCP II and photosystem II core as it is evidenced from lowering of the Mg2+ induced changes of the short wavelength fluorescence intensity and increase in the relative quantum requirement values. The results are discussed in connection with a possible effect of paraquat on PS II.
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Dahlin, Clas. « Immunogold localization of LHC II proteins in chloroplasts with different degrees of grana stacking induced by SAN-9789. » Physiologia Plantarum 76, no 3 (juillet 1989) : 438–44. http://dx.doi.org/10.1111/j.1399-3054.1989.tb06216.x.
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Zolla, Lello, Maria Bianchetti, Anna Maria Timperio, Giuseppe Scarascia Mugnozza et Danilo Corradini. « Capillary electrophoresis of closely related intrinsic thylakoid membrane proteins of the photosystem II light-harvesting complex (LHC II) ». Electrophoresis 17, no 10 (1996) : 1597–601. http://dx.doi.org/10.1002/elps.1150171018.
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Lyu, Guizhen, Dongbing Li, Hui Xiong, Langtao Xiao, Jianhua Tong, Chanjuan Ning, Ping Wang et Shaoshan Li. « Quantitative Proteomic Analyses Identify STO/BBX24 -Related Proteins Induced by UV-B ». International Journal of Molecular Sciences 21, no 7 (3 avril 2020) : 2496. http://dx.doi.org/10.3390/ijms21072496.
Texte intégralRésumé :
Plants use solar radiation for photosynthesis and are inevitably exposed to UV-B. To adapt to UV-B radiation, plants have evolved a sophisticated strategy, but the mechanism is not well understood. We have previously reported that STO (salt tolerance)/BBX24 is a negative regulator of UV-B-induced photomorphogenesis. However, there is limited knowledge of the regulatory network of STO in UV-B signaling. Here, we report the identification of proteins differentially expressed in the wild type (WT) and sto mutant after UV-B radiation by iTRAQ (isobaric tags for relative and absolute quantitation)-based proteomic analysis to explore differential proteins that depend on STO and UV-B signaling. A total of 8212 proteins were successfully identified, 221 of them were STO-dependent proteins in UV-B irradiated plants. The abundances of STO-dependent PSB and LHC (light-harvesting complex) proteins in sto mutants decreased under UV-B radiation, suggesting that STO is necessary to maintain the normal accumulation of photosynthetic system complex under UV-B radiation to facilitate photosynthesis photon capture. The abundance of phenylalanine lyase-1 (PAL1), chalcone synthetase (CHS), and flavonoid synthetase (FLS) increased significantly after UV-B irradiation, suggesting that the accumulation of flavonoids do not require STO, but UV-B is needed. Under UV-B radiation, STO stabilizes the structure of antenna protein complex by maintaining the accumulation of PSBs and LHCs, thereby enhancing the non-photochemical quenching (NPQ) ability, releasing extra energy, protecting photosynthesis, and ultimately promoting the elongation of hypocotyl. The accumulation of flavonoid synthesis key proteins is independent of STO under UV-B radiation. Overall, our results provide a comprehensive regulatory network of STO in UV-B signaling.
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Li, Xiu, Rui Yang, Liulong Li, Ke Liu, Matthew Tom Harrison, Shah Fahad, Mingmei Wei, Lijun Yin, Meixue Zhou et Xiaoyan Wang. « Physiological and Molecular Responses of Wheat to Low Light Intensity ». Agronomy 13, no 1 (16 janvier 2023) : 272. http://dx.doi.org/10.3390/agronomy13010272.
Texte intégralRésumé :
Here we document physiological and molecular attributes of three wheat cultivars (ZM9023, YM158 and FM1228) under low light intensity with advanced technologies, including non-standard quantitative technology and quantitative proteomics technology. We found lower dry matter accumulation of YM158 compared with ZM 9023 and FM1228 under low light intensities due to up-regulation of photosynthetic parameters electron transport rate (ETR), Y(II), Fv/Fm, Chl (a + b) of YM158 and down-regulation of Chl a/b. ETR, Y(II) and Fv/Fm significantly decreased between ZM9023 and FM1228. The ETR between PSII and PSI of YM158 increased, while light use efficiency (LUE) of ZM9023 and FM1228 decreased. We found that YM158 had greater propensity to adapt to low light compared with ZM9023, as the former was able to increase photochemical electron transfer rate, enhance photosystem activity, and increase the light energy under low light. This meant that the YM158 flag leaf has stronger regulatory mechanism under low light environment. Through proteomic analysis, we found LHC protein (LHCB1, LHCB4, LHCA2, LHCA3) for YH158 was significantly up-regulated, while the PSII subunit protein of FM1228 and ZM9023 b559 subunit protein were down-regulated. We also documented enhanced light use efficiency (LUE) due to higher light capture pigment protein complex (LHC), photosystem II (PSII), PSI and cytochrome B6F-related proteins, with dry matter accumulation being positively correlated with Fv/Fm, ETR, and ΦPS(II), and negatively correlated with initial fluorescence F0. We suggest that Fv/Fm, ETR, and ΦPS(II) could be considered in shade tolerance screening to facilitate wheat breeding.
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Mihailova, Gergana, Nikolai K. Christov, Éva Sárvári, Ádám Solti, Richard Hembrom, Katalin Solymosi, Áron Keresztes et al. « Reactivation of the Photosynthetic Apparatus of Resurrection Plant Haberlea rhodopensis during the Early Phase of Recovery from Drought- and Freezing-Induced Desiccation ». Plants 11, no 17 (23 août 2022) : 2185. http://dx.doi.org/10.3390/plants11172185.
Texte intégralRésumé :
Haberlea rhodopensis is a unique desiccation-tolerant angiosperm that also survives winter frost. As, upon freezing temperatures, H. rhodopensis desiccates, the taxon is proposed to survive low temperature stress using its desiccation tolerance mechanisms. To reveal the validity of this hypothesis, we analyzed the structural alterations and organization of photosynthetic apparatus during the first hours of recovery after drought- and freezing-induced desiccation. The dynamics of the ultrastructure remodeling in the mesophyll cells and the restoration of the thylakoid membranes shared similarities independent of the reason for desiccation. Among the most obvious changes in thylakoid complexes, the proportion of the PSI-LHCII complex strongly increased around 70% relative water content (RWC), whereas the proportion of Lhc monomers decreased from the beginning of rehydration. We identified enhanced levels of cyt b6f complex proteins that contributed to the enhanced electron flow. The high abundance of proteins related to excitation energy dissipation, PsbS, Lhcb5, Lhcb6 and ELIPs, together with the increased content of dehydrins contributed to the preservation of cellular integrity. ELIP expression was maintained at high levels up to 9 h into recovery. Although the recovery processes from drought- and freezing-induced desiccation were found to be similar in progress and time scale, slight variations indicate that they are not identical.
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Teramoto, Haruhiko, Akira Nakamori, Jun Minagawa et Taka-aki Ono. « Light-Intensity-Dependent Expression of Lhc Gene Family Encoding Light-Harvesting Chlorophyll-a/b Proteins of Photosystem II in Chlamydomonas reinhardtii ». Plant Physiology 130, no 1 (8 août 2002) : 325–33. http://dx.doi.org/10.1104/pp.004622.
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Stauber, Einar J., Andreas Fink, Christine Markert, Olaf Kruse, Udo Johanningmeier et Michael Hippler. « Proteomics of Chlamydomonas reinhardtii Light-Harvesting Proteins ». Eukaryotic Cell 2, no 5 (octobre 2003) : 978–94. http://dx.doi.org/10.1128/ec.2.5.978-994.2003.
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ABSTRACT With the recent development of techniques for analyzing transmembrane thylakoid proteins by two-dimensional gel electrophoresis, systematic approaches for proteomic analyses of membrane proteins became feasible. In this study, we established detailed two-dimensional protein maps of Chlamydomonas reinhardtii light-harvesting proteins (Lhca and Lhcb) by extensive tandem mass spectrometric analysis. We predicted eight distinct Lhcb proteins. Although the major Lhcb proteins were highly similar, we identified peptides which were unique for specific lhcbm gene products. Interestingly, lhcbm6 gene products were resolved as multiple spots with different masses and isoelectric points. Gene tagging experiments confirmed the presence of differentially N-terminally processed Lhcbm6 proteins. The mass spectrometric data also revealed differentially N-terminally processed forms of Lhcbm3 and phosphorylation of a threonine residue in the N terminus. The N-terminal processing of Lhcbm3 leads to the removal of the phosphorylation site, indicating a potential novel regulatory mechanism. At least nine different lhca-related gene products were predicted by comparison of the mass spectrometric data against Chlamydomonas expressed sequence tag and genomic databases, demonstrating the extensive variability of the C. reinhardtii Lhca antenna system. Out of these nine, three were identified for the first time at the protein level. This proteomic study demonstrates the complexity of the light-harvesting proteins at the protein level in C. reinhardtii and will be an important basis of future functional studies addressing this diversity.
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Fujiyoshi, Y., K. Murata, K. Mitsuoka, T. Hirai, A. Miyazawa et Y. Kimura. « A microscopic system for high-resolution electron crystallography ». Proceedings, annual meeting, Electron Microscopy Society of America 53 (13 août 1995) : 70–71. http://dx.doi.org/10.1017/s0424820100136726.
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High-resolution electron cryo-microscopy is one of good candidate for structure analysis of membrane-protein, and also actually analyzed the structure of membrane-proteins such as bacteriorhodopsin (bR) and plant light-harvesting complex (LHC). By developing an expeditious method for structure analysis up to atomic or near atomic resolution, we would like to interpret a function of protein from the structural point of view. However, there are some difficulties in electron microscopy for structure analysis of protein. Especially, the most serious problems are the specimen damage caused by electron irradiation, the denaturation of biomolecules caused by dehydration and missing high-resolution data on electron micrographs at high-tilted angle.The irradiation damage at 8K has been found to be reduced to 1/20 compared with that at room temperature. We have, therefore, developed a high-resolution electron cryo-microscope and improved it by which images can be recorded with higher resolution than 3 Å at a specimen-stage temperature of 4.2 K, even when the specimen is highly tilted. The highly tilted data are essential for reduction of the missing corn effect.
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Jansson, Stefan, et Petter Gustafsson. « Evolutionary conservation of the chlorophyll a/b-binding proteins cDNAs encoding Type I, II and III LHC I polypeptides from the gymnosperm Scots pine ». Molecular and General Genetics MGG 229, no 1 (septembre 1991) : 67–76. http://dx.doi.org/10.1007/bf00264214.
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Tajmir-Riahi, H. A., et A. Ahmed. « Complexation of copper and zinc ions with proteins of a light-harvesting complex (LHC-II) of chloroplast thylakoid membranes studied by FT-IR spectroscopy ». Journal of Molecular Structure 297 (août 1993) : 103–8. http://dx.doi.org/10.1016/0022-2860(93)80164-q.
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Alomrani, Sarah, Karl J. Kunert et Christine H. Foyer. « Papain-like cysteine proteases are required for the regulation of photosynthetic gene expression and acclimation to high light stress ». Journal of Experimental Botany 72, no 9 (4 mars 2021) : 3441–54. http://dx.doi.org/10.1093/jxb/erab101.
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AbstractChloroplasts are considered to be devoid of cysteine proteases. Using transgenic Arabidopsis lines expressing the rice cystatin, oryzacystatin I (OC-I), in the chloroplasts (PC lines) or cytosol (CYS lines), we explored the hypothesis that cysteine proteases regulate photosynthesis. The CYS and PC lines flowered later than the wild type (WT) and accumulated more biomass after flowering. In contrast to the PC rosettes, which accumulated more leaf chlorophyll and carotenoid pigments than the WT, the CYS lines had lower amounts of leaf pigments. High-light-dependent decreases in photosynthetic carbon assimilation and the abundance of the Rubisco large subunit protein, the D1 protein, and the phosphorylated form of D1 proteins were attenuated in the CYS lines and reversed in the PC lines relative to the WT. However, the transgenic lines had higher amounts of LHC, rbcs, pasbA, and pasbD transcripts than the WT, and also showed modified chloroplast to nucleus signalling. We conclude that cysteine proteases accelerate the reconfiguration of the chloroplast proteome after flowering and in response to high-light stress. Inhibition of cysteine proteases, such as AtCEP1, slows chloroplast protein degradation and stimulates photosynthetic gene expression and chloroplast to nucleus signalling, enhancing stress tolerance traits.
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Saccon, Francesco, Vasco Giovagnetti, Mahendra K. Shukla et Alexander V. Ruban. « Rapid regulation of photosynthetic light harvesting in the absence of minor antenna and reaction centre complexes ». Journal of Experimental Botany 71, no 12 (9 mars 2020) : 3626–37. http://dx.doi.org/10.1093/jxb/eraa126.
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Abstract Plants are subject to dramatic fluctuations in the intensity of sunlight throughout the day. When the photosynthetic machinery is exposed to high light, photons are absorbed in excess, potentially leading to oxidative damage of its delicate membrane components. A photoprotective molecular process called non-photochemical quenching (NPQ) is the fastest response carried out in the thylakoid membranes to harmlessly dissipate excess light energy. Despite having been intensely studied, the site and mechanism of this essential regulatory process are still debated. Here, we show that the main NPQ component called energy-dependent quenching (qE) is present in plants with photosynthetic membranes largely enriched in the major trimeric light-harvesting complex (LHC) II, while being deprived of all minor LHCs and most photosystem core proteins. This fast and reversible quenching depends upon thylakoid lumen acidification (ΔpH). Enhancing ΔpH amplifies the extent of the quenching and restores qE in the membranes lacking PSII subunit S protein (PsbS), whereas the carotenoid zeaxanthin modulates the kinetics and amplitude of the quenching. These findings highlight the self-regulatory properties of the photosynthetic light-harvesting membranes in vivo, where the ability to switch reversibly between the harvesting and dissipative states is an intrinsic property of the major LHCII.
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Garczarek, Laurence, Anne Poupon et Frédéric Partensky. « Origin and evolution of transmembrane Chl-binding proteins : hydrophobic cluster analysis suggests a common one-helix ancestor for prokaryotic (Pcb) and eukaryotic (LHC) antenna protein superfamilies ». FEMS Microbiology Letters 222, no 1 (mai 2003) : 59–68. http://dx.doi.org/10.1016/s0378-1097(03)00241-6.
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Choi, Dongsu, Woongsoon Jang, Hiroto Toda et Masato Yoshikawa. « Differences in Characteristics of Photosynthesis and Nitrogen Utilization in Leaves of the Black Locust (Robinia pseudoacacia L.) According to Leaf Position ». Forests 12, no 3 (16 mars 2021) : 348. http://dx.doi.org/10.3390/f12030348.
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Robinia pseudoacacia L. has been widely planted worldwide for a variety of purposes, but it is a nonindigenous species currently invading the central part of Japanese river terraces. To understand and control this invasion, we investigated how this species invests nitrogen resources in different functions depending on the leaf location, and how these resources are used in physiological reactions such as photosynthesis. The Tama river terrace was examined in Tokyo, Japan. The leaf nitrogen (N) concentration, chlorophyll (Chl) concentration, Chl a/b ratio, leaf mass per unit area (LMA) and ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCo) concentration were all significantly lower in shade leaves than in leaves exposed to the sun. Conversely, the net photosynthetic rate in saturated light conditions (Pmax), the net photosynthetic rate under enhanced CO2 concentration and light saturation (Amax), the maximum carboxylation rate of RuBisCo (Vcmax) and the maximum rate of electron transport driving RUBP regeneration (Jmax) were all significantly lower in shade leaves than in leaves exposed to the sun. We also found that RuBisCo/N and Chl/N were significantly less in shade leaves, and values of Jmax/N, Vcmax/N less in shade leaves than in sun leaves, but not significantly. Allocation of nitrogen in leaves to photosynthetic proteins, RuBisCo (NR) was broadly less in shade leaves, and NL (light-harvesting complex: LHC, photosystem I and II: PSI and PSII) and NE (electron transport) were also lower. The N remaining was much greater in shade leaves than in sun leaves. We suggest that N remobilization from RuBisCo is more efficient than remobilization from proteins of NE, and from NL. This study shows that R. pseudoacacia has an enhanced ability to adapt to environmental changes via characteristic changes in N allocation trade-offs and physiological traits in its sun and shade leaves.
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Grebe, Steffen, Andrea Trotta, Azfar A. Bajwa, Marjaana Suorsa, Peter J. Gollan, Stefan Jansson, Mikko Tikkanen et Eva-Mari Aro. « The unique photosynthetic apparatus of Pinaceae : analysis of photosynthetic complexes in Picea abies ». Journal of Experimental Botany 70, no 12 (2 avril 2019) : 3211–25. http://dx.doi.org/10.1093/jxb/erz127.
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Abstract Pinaceae are the predominant photosynthetic species in boreal forests, but so far no detailed description of the protein components of the photosynthetic apparatus of these gymnosperms has been available. In this study we report a detailed characterization of the thylakoid photosynthetic machinery of Norway spruce (Picea abies (L.) Karst). We first customized a spruce thylakoid protein database from translated transcript sequences combined with existing protein sequences derived from gene models, which enabled reliable tandem mass spectrometry identification of P. abies thylakoid proteins from two-dimensional large pore blue-native/SDS-PAGE. This allowed a direct comparison of the two-dimensional protein map of thylakoid protein complexes from P. abies with the model angiosperm Arabidopsis thaliana. Although the subunit composition of P. abies core PSI and PSII complexes is largely similar to that of Arabidopsis, there was a high abundance of a smaller PSI subcomplex, closely resembling the assembly intermediate PSI* complex. In addition, the evolutionary distribution of light-harvesting complex (LHC) family members of Pinaceae was compared in silico with other land plants, revealing that P. abies and other Pinaceae (also Gnetaceae and Welwitschiaceae) have lost LHCB4, but retained LHCB8 (formerly called LHCB4.3). The findings reported here show the composition of the photosynthetic apparatus of P. abies and other Pinaceae members to be unique among land plants.
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Girolomoni, Laura, Stefano Cazzaniga, Alberta Pinnola, Federico Perozeni, Matteo Ballottari et Roberto Bassi. « LHCSR3 is a nonphotochemical quencher of both photosystems inChlamydomonas reinhardtii ». Proceedings of the National Academy of Sciences 116, no 10 (19 février 2019) : 4212–17. http://dx.doi.org/10.1073/pnas.1809812116.
Texte intégralRésumé :
Photosynthetic organisms prevent oxidative stress from light energy absorbed in excess through several photoprotective mechanisms. A major component is thermal dissipation of chlorophyll singlet excited states and is called nonphotochemical quenching (NPQ). NPQ is catalyzed in green algae by protein subunits called LHCSRs (Light Harvesting Complex Stress Related), homologous to the Light Harvesting Complexes (LHC), constituting the antenna system of both photosystem I (PSI) and PSII. We investigated the role of LHCSR1 and LHCSR3 in NPQ activation to verify whether these proteins are involved in thermal dissipation of PSI excitation energy, in addition to their well-known effect on PSII. To this aim, we measured the fluorescence emitted at 77 K by whole cells in a quenched or unquenched state, using green fluorescence protein as the internal standard. We show that NPQ activation by high light treatment inChlamydomonas reinhardtiileads to energy quenching in both PSI and PSII antenna systems. By analyzing quenching properties of mutants affected on the expression of LHCSR1 or LHCSR3 gene products and/or state 1–state 2 transitions or zeaxanthin accumulation, namely,npq4,stt7,stt7 npq4,npq4 lhcsr1,lhcsr3-complementednpq4 lhcsr1andnpq1, we showed that PSI undergoes NPQ through quenching of the associated LHCII antenna. This quenching event is fast-reversible on switching the light off, is mainly related to LHCSR3 activity, and is dependent on thylakoid luminal pH. Moreover, PSI quenching could also be observed in the absence of zeaxanthin or STT7 kinase activity.
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Küpper, Hendrik, Ivan Šetlík, Eva Šetliková, Naila Ferimazova, Martin Spiller et Frithjof C. Küpper. « Copper-induced inhibition of photosynthesis : limiting steps of in vivo copper chlorophyll formation in Scenedesmus quadricauda ». Functional Plant Biology 30, no 12 (2003) : 1187. http://dx.doi.org/10.1071/fp03129.
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The in vivo substitution of Mg2+ in chlorophyll by heavy metals is an important damage mechanism in heavy metal-stressed plants that leads to an inhibition of photosynthesis. In photosynthetic organisms with LHC II antennae, the in vivo substitution of Mg2+ by Cu2+ occurs particularly readily under low irradiance with a dark phase — a phenomenon referred to as 'shade reaction'. In the present study the limiting steps of the shade reaction were investigated with synchronised cultures of the chlorococcal green alga Scenedesmus quadricauda (Turp.) Bréb. The rate of copper chlorophyll formation during shade reaction was shown to be controlled by several factors; firstly, in some phases of the cell cycle, especially at the end of the light period, Mg2+ in chlorophyll was not accessible to substitution. This pattern is likely to be caused by cell cycle-dependent changes in photosynthesis and thylakoid ultrastructure, which were published earlier and are reconsidered in the discussion of the present work. Secondly, prolonged culture in a medium containing 3 μM Cu2+ reversibly increased the resistance of the strain to Cu2+. Culturing without added Cu2+ lowered the threshold concentrations of various deleterious effects more than 10-fold within 8 months of de-adaptation. Adaptation to high Cu2+ levels is discussed in the context of studies of the regulation of metal transporter proteins. In addition, it was also observed that toxic Cu2+ levels impaired photosynthesis sooner than cell division.
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Pi, Xiong, Lirong Tian, Huai-En Dai, Xiaochun Qin, Lingpeng Cheng, Tingyun Kuang, Sen-Fang Sui et Jian-Ren Shen. « Unique organization of photosystem I–light-harvesting supercomplex revealed by cryo-EM from a red alga ». Proceedings of the National Academy of Sciences 115, no 17 (9 avril 2018) : 4423–28. http://dx.doi.org/10.1073/pnas.1722482115.
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Photosystem I (PSI) is one of the two photosystems present in oxygenic photosynthetic organisms and functions to harvest and convert light energy into chemical energy in photosynthesis. In eukaryotic algae and higher plants, PSI consists of a core surrounded by variable species and numbers of light-harvesting complex (LHC)I proteins, forming a PSI-LHCI supercomplex. Here, we report cryo-EM structures of PSI-LHCR from the red alga Cyanidioschyzon merolae in two forms, one with three Lhcr subunits attached to the side, similar to that of higher plants, and the other with two additional Lhcr subunits attached to the opposite side, indicating an ancient form of PSI-LHCI. Furthermore, the red algal PSI core showed features of both cyanobacterial and higher plant PSI, suggesting an intermediate type during evolution from prokaryotes to eukaryotes. The structure of PsaO, existing in eukaryotic organisms, was identified in the PSI core and binds three chlorophylls a and may be important in harvesting energy and in mediating energy transfer from LHCII to the PSI core under state-2 conditions. Individual attaching sites of LHCRs with the core subunits were identified, and each Lhcr was found to contain 11 to 13 chlorophylls a and 5 zeaxanthins, which are apparently different from those of LHCs in plant PSI-LHCI. Together, our results reveal unique energy transfer pathways different from those of higher plant PSI-LHCI, its adaptation to the changing environment, and the possible changes of PSI-LHCI during evolution from prokaryotes to eukaryotes.
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Mey, Jacob T., Brian K. Blackburn, Edwin R. Miranda, Alec B. Chaves, Joan Briller, Marcelo G. Bonini et Jacob M. Haus. « Dicarbonyl stress and glyoxalase enzyme system regulation in human skeletal muscle ». American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 314, no 2 (1 février 2018) : R181—R190. http://dx.doi.org/10.1152/ajpregu.00159.2017.
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Skeletal muscle insulin resistance is a hallmark of Type 2 diabetes (T2DM) and may be exacerbated by protein modifications by methylglyoxal (MG), known as dicarbonyl stress. The glyoxalase enzyme system composed of glyoxalase 1/2 (GLO1/GLO2) is the natural defense against dicarbonyl stress, yet its protein expression, activity, and regulation remain largely unexplored in skeletal muscle. Therefore, this study investigated dicarbonyl stress and the glyoxalase enzyme system in the skeletal muscle of subjects with T2DM (age: 56 ± 5 yr.; BMI: 32 ± 2 kg/m2) compared with lean healthy control subjects (LHC; age: 27 ± 1 yr.; BMI: 22 ± 1 kg/m2). Skeletal muscle biopsies obtained from the vastus lateralis at basal and insulin-stimulated states of the hyperinsulinemic (40 mU·m−2·min−1)–euglycemic (5 mM) clamp were analyzed for proteins related to dicarbonyl stress and glyoxalase biology. At baseline, T2DM had increased carbonyl stress and lower GLO1 protein expression (−78.8%), which inversely correlated with BMI, percent body fat, and HOMA-IR, while positively correlating with clamp-derived glucose disposal rates. T2DM also had lower NRF2 protein expression (−31.6%), which is a positive regulator of GLO1, while Keap1 protein expression, a negative regulator of GLO1, was elevated (207%). Additionally, insulin stimulation during the clamp had a differential effect on NRF2, Keap1, and MG-modified protein expression. These data suggest that dicarbonyl stress and the glyoxalase enzyme system are dysregulated in T2DM skeletal muscle and may underlie skeletal muscle insulin resistance. Whether these phenotypic differences contribute to the development of T2DM warrants further investigation.
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Giardi, M. T., J. Barber, M. C. Giardina et R. Bassi. « Studies on the Herbicide Binding Site in Isolated Photosystem II Core Complexes from a Flat-Bed Isoelectrofocusing Method ». Zeitschrift für Naturforschung C 45, no 5 (1 mai 1990) : 366–72. http://dx.doi.org/10.1515/znc-1990-0510.
Texte intégralRésumé :
Abstract Isoelectrofocusing has been used to separate various chlorophyll-protein complexes of photosystem two (PS II). Light-harvesting complexes containing chlorophyll a and chlorophyll b (LHC II) were located in bands having p/s in the region of 4.5. At slightly higher pH other light-harvesting complexes containing little or no chlorophyll b were found. In the most basic region of the isoelectrofocusing gel, were located PS II core complexes characterized by containing the proteins of CP47, CP43, D 1, D 2 and α-subunit of cytochrome b559. The number of PS II core bands depended on the particular conditions employed for the separation procedure and in some cases were contaminated by CP 29. It is suggested that this heterogeneity resulting from different protonation states of the PS II. The least-acidic PS II core complex (pI 5.5) was found to bind the herbicides atrazine, diuron and dinoseb. In contrast, a PS II core complex with a p / of 4.9 bound only diuron. Its inability to bind atrazine was shown to be due to the low pH but no such explanation could be found for dinoseb. When atrazine-resistant mutant Senecio vulgaris was used, no binding of radioactive atra zine was observed with the PS II cores having a p i of 5.5. It is therefore suggested that the normal atrazine binding observed with PS II cores involves the high affinity site detected with intact membranes. With the PS II cores, however, this site has a reduced affinity probably due to structural modification in the D 1-polypeptide resulting from the isolation procedures.
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Marabini, Roberto, Gabriela N. Condezo, Mart Krupovic, Rosa Menéndez-Conejero, Josué Gómez-Blanco et Carmen San Martín. « Near-atomic structure of an atadenovirus reveals a conserved capsid-binding motif and intergenera variations in cementing proteins ». Science Advances 7, no 14 (mars 2021) : eabe6008. http://dx.doi.org/10.1126/sciadv.abe6008.
Texte intégralRésumé :
Of five known adenovirus genera, high-resolution structures are available only for mammalian-infecting mastadenoviruses. We present the first high-resolution structure of an adenovirus with nonmammalian host: lizard atadenovirus LAdV-2. We find a large conformational difference in the internal vertex protein IIIa between mast- and atadenoviruses, induced by the presence of an extended polypeptide. This polypeptide, and α-helical clusters beneath the facet, likely correspond to genus-specific proteins LH2 and p32k. Another genus-specific protein, LH3, with a fold typical of bacteriophage tailspikes, contacts the capsid surface via a triskelion structure identical to that used by mastadenovirus protein IX, revealing a conserved capsid-binding motif and an ancient gene duplication event. Our data also suggest that mastadenovirus E1B-55 K was exapted from the atadenovirus-like LH3 protein. This work provides new information on the evolution of adenoviruses, emphasizing the importance of minor coat proteins for determining specific physicochemical properties of virions and most likely their tropism.
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Köhler, J., A. M. van Oijen, M. Ketelaars, C. Hofmann, M. Matsushita, T. J. Aartsma et J. Schmidt. « Optical Spectroscopy of Individual Photosynthetic Pigment Protein Complexes ». International Journal of Modern Physics B 15, no 28n30 (10 décembre 2001) : 3633–36. http://dx.doi.org/10.1142/s0217979201008317.
Texte intégralRésumé :
Photosynthesis is the process by which plants, algae and photosynthetic bacteria convert solar energy into a form that can be used to sustain the life process. The light reactions occur in closely coupled pigment systems. The energy is absorbed by a network of antenna pigment proteins and efficiently transferred to the photochemical reaction centre where a charge separation takes place providing the free energy for subsequent chemical reactions. The total conversion process, starting with the absorption of a photon and ending with a stable charge separated state occurs within less than 50 ps and has an overall quantum yield of more than 90%. The success of this natural process is based on both the highly efficient absorption of photons by the light-harvesting antenna system and the rapid and efficient transfer of excitation energy to the reaction centre. It is known that most photosynthetic purple bacteria contain two types of antenna complexes, light-harvesting complex 1 (LH1) and light harvesting complex 2 (LH2) which both have a ring-like structure [1,2]. (Some bacterial species like Rhodopseudomonas acidophila contain a third light-harvesting complex termed B800-820.) The reaction centre (RC) presumably forms the core of the LH1 complex, while LH2 complexes are arranged around the perimeter of the LH1 ring in a two-dimensional structure. However the full three-dimensional structure of the whole photosynthetic unit is as yet unknown. The absorption of a photon (mainly) takes place in the LH2 pigments followed by a fast transfer of the excitation energy to the LH1 complex and subsequently to the reaction centre. It appears that the whole structure is highly optimized for capturing light energy and to funnel it to the reaction centre [3-7].
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Kume, Atsushi, Tomoko Akitsu et Kenlo Nishida Nasahara. « Why is chlorophyll b only used in light-harvesting systems ? » Journal of Plant Research 131, no 6 (10 juillet 2018) : 961–72. http://dx.doi.org/10.1007/s10265-018-1052-7.
Texte intégralRésumé :
Abstract Chlorophylls (Chl) are important pigments in plants that are used to absorb photons and release electrons. There are several types of Chls but terrestrial plants only possess two of these: Chls a and b. The two pigments form light-harvesting Chl a/b-binding protein complexes (LHC), which absorb most of the light. The peak wavelengths of the absorption spectra of Chls a and b differ by c. 20 nm, and the ratio between them (the a/b ratio) is an important determinant of the light absorption efficiency of photosynthesis (i.e., the antenna size). Here, we investigated why Chl b is used in LHCs rather than other light-absorbing pigments that can be used for photosynthesis by considering the solar radiation spectrum under field conditions. We found that direct and diffuse solar radiation (PARdir and PARdiff, respectively) have different spectral distributions, showing maximum spectral photon flux densities (SPFD) at c. 680 and 460 nm, respectively, during the daytime. The spectral absorbance spectra of Chls a and b functioned complementary to each other, and the absorbance peaks of Chl b were nested within those of Chl a. The absorption peak in the short wavelength region of Chl b in the proteinaceous environment occurred at c. 460 nm, making it suitable for absorbing the PARdiff, but not suitable for avoiding the high spectral irradiance (SIR) waveband of PARdir. In contrast, Chl a effectively avoided the high SPFD and/or high SIR waveband. The absorption spectra of photosynthetic complexes were negatively correlated with SPFD spectra, but LHCs with low a/b ratios were more positively correlated with SIR spectra. These findings indicate that the spectra of the photosynthetic pigments and constructed photosystems and antenna proteins significantly align with the terrestrial solar spectra to allow the safe and efficient use of solar radiation.
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Satya Lakshmi, O., et N. M. Rao. « Evolving Lac repressor for enhanced inducibility ». Protein Engineering, Design and Selection 22, no 2 (21 novembre 2008) : 53–58. http://dx.doi.org/10.1093/protein/gzn069.
Texte intégral
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Takshi, Arash, Houman Yaghoubi, Daniel Jun et J. Thomas Beatty. « Bio-Phototransistors with Immobilized Photosynthetic Proteins ». Electronics 9, no 10 (18 octobre 2020) : 1709. http://dx.doi.org/10.3390/electronics9101709.
Texte intégralRésumé :
The efficient mechanism of light capture by photosynthetic proteins allows for energy transfer and conversion to electrochemical energy at very low light intensities. In this work, reaction center (RC) proteins, or a core complex consisting of the RC encircled by light harvesting (LH1) proteins (RC-LH1) from photosynthetic bacteria, were immobilized on an insulating layer of an ion-sensitive field-effect transistor (ISFET) to build bio-photodetectors. The orientation of the RC proteins was controlled via application of a hybrid linker made of 10-carboxydecylphosphonic acid and cytochrome c that anchored the RCs to their electron donor side. Bio-phototransistors consisting of either the core RC or the RC-LH1 core complex were tested under white and monochromic light. The difference between the dark and light currents at different wavelengths are well-matched with the absorption spectrum of the photosynthetic proteins. The results show potential for the use of photosynthetic proteins in photodetectors.
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Sabari, Sarizan, Norliza Julmohammad, Haque Akanda Md Jahurul, Patricia Matanjun et Noorakmar Ab. Wahab. « In Vitro Infant Digestion of Whey Proteins Isolate–Lactose ». Foods 12, no 3 (3 février 2023) : 667. http://dx.doi.org/10.3390/foods12030667.
Texte intégralRésumé :
The model in vitro protein digestion technique has received greater attention due to providing significant advantages compared to in vivo experiments. This research employed an in vitro infant digestive static model to examine the protein digestibility of whey proteins isolate–lactose (WPI–Lac). The polyacrylamide gel electrophoresis (PAGE) pattern for alpha-lactalbumin of WPI at 60 min showed no detectable bands, while the alpha-lactalbumin of the WPI–Lac was completely digested after 5 min of gastric digestion. The beta-lactoglobulin of the WPI–Lac was found to be similar to the beta-lactoglobulin of the WPI, being insignificant at pH 3.0. The alpha-lactalbumin of the WPI decreased after 100 min of duodenal digestion at pH 6.5, and the WPI–Lac was completely digested after 60 min. The peptides were identified as ~2 kilodalton (kDa) in conjugated protein, which indicated that the level of degradation of the protein was high, due to the hydrolysis progress. The conjugated protein increased the responsiveness to digestive proteolysis, potentially leading to the release of immunogenic protein by lactose, and to the creation of hypoallergenic protein.
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Levens, D., et P. M. Howley. « Novel method for identifying sequence-specific DNA-binding proteins ». Molecular and Cellular Biology 5, no 9 (septembre 1985) : 2307–15. http://dx.doi.org/10.1128/mcb.5.9.2307-2315.1985.
Texte intégralRésumé :
We developed a general method for the enrichment and identification of sequence-specific DNA-binding proteins. A well-characterized protein-DNA interaction is used to isolate from crude cellular extracts or fractions thereof proteins which bind to specific DNA sequences; the method is based solely on this binding property of the proteins. The DNA sequence of interest, cloned adjacent to the lac operator DNA segment is incubated with a lac repressor-beta-galactosidase fusion protein which retains full operator and inducer binding properties. The DNA fragment bound to the lac repressor-beta-galactosidase fusion protein is precipitated by the addition of affinity-purified anti-beta-galactosidase immobilized on beads. This forms an affinity matrix for any proteins which might interact specifically with the DNA sequence cloned adjacent to the lac operator. When incubated with cellular extracts in the presence of excess competitor DNA, any protein(s) which specifically binds to the cloned DNA sequence of interest can be cleanly precipitated. When isopropyl-beta-D-thiogalactopyranoside is added, the lac repressor releases the bound DNA, and thus the protein-DNA complex consisting of the specific restriction fragment and any specific binding protein(s) is released, permitting the identification of the protein by standard biochemical techniques. We demonstrate the utility of this method with the lambda repressor, another well-characterized DNA-binding protein, as a model. In addition, with crude preparations of the yeast mitochondrial RNA polymerase, we identified a 70,000-molecular-weight peptide which binds specifically to the promoter region of the yeast mitochondrial 14S rRNA gene.
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Levens, D., et P. M. Howley. « Novel method for identifying sequence-specific DNA-binding proteins. » Molecular and Cellular Biology 5, no 9 (septembre 1985) : 2307–15. http://dx.doi.org/10.1128/mcb.5.9.2307.
Texte intégralRésumé :
We developed a general method for the enrichment and identification of sequence-specific DNA-binding proteins. A well-characterized protein-DNA interaction is used to isolate from crude cellular extracts or fractions thereof proteins which bind to specific DNA sequences; the method is based solely on this binding property of the proteins. The DNA sequence of interest, cloned adjacent to the lac operator DNA segment is incubated with a lac repressor-beta-galactosidase fusion protein which retains full operator and inducer binding properties. The DNA fragment bound to the lac repressor-beta-galactosidase fusion protein is precipitated by the addition of affinity-purified anti-beta-galactosidase immobilized on beads. This forms an affinity matrix for any proteins which might interact specifically with the DNA sequence cloned adjacent to the lac operator. When incubated with cellular extracts in the presence of excess competitor DNA, any protein(s) which specifically binds to the cloned DNA sequence of interest can be cleanly precipitated. When isopropyl-beta-D-thiogalactopyranoside is added, the lac repressor releases the bound DNA, and thus the protein-DNA complex consisting of the specific restriction fragment and any specific binding protein(s) is released, permitting the identification of the protein by standard biochemical techniques. We demonstrate the utility of this method with the lambda repressor, another well-characterized DNA-binding protein, as a model. In addition, with crude preparations of the yeast mitochondrial RNA polymerase, we identified a 70,000-molecular-weight peptide which binds specifically to the promoter region of the yeast mitochondrial 14S rRNA gene.