Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 17 de 17
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Elife ; 102021 10 19.
Artigo em Inglês | MEDLINE | ID: mdl-34665128

RESUMO

Enzymerhodopsins represent a recently discovered class of rhodopsins which includes histidine kinase rhodopsin, rhodopsin phosphodiesterases, and rhodopsin guanylyl cyclases (RGCs). The regulatory influence of the rhodopsin domain on the enzyme activity is only partially understood and holds the key for a deeper understanding of intra-molecular signaling pathways. Here, we present a UV-Vis and FTIR study about the light-induced dynamics of a RGC from the fungus Catenaria anguillulae, which provides insights into the catalytic process. After the spectroscopic characterization of the late rhodopsin photoproducts, we analyzed truncated variants and revealed the involvement of the cytosolic N-terminus in the structural rearrangements upon photo-activation of the protein. We tracked the catalytic reaction of RGC and the free GC domain independently by UV-light induced release of GTP from the photolabile NPE-GTP substrate. Our results show substrate binding to the dark-adapted RGC and GC alike and reveal differences between the constructs attributable to the regulatory influence of the rhodopsin on the conformation of the binding pocket. By monitoring the phosphate rearrangement during cGMP and pyrophosphate formation in light-activated RGC, we were able to confirm the M state as the active state of the protein. The described setup and experimental design enable real-time monitoring of substrate turnover in light-activated enzymes on a molecular scale, thus opening the pathway to a deeper understanding of enzyme activity and protein-protein interactions.


Assuntos
Blastocladiomycota/genética , GMP Cíclico/genética , Proteínas Fúngicas/genética , Guanilato Ciclase/genética , Rodopsina/genética , Blastocladiomycota/metabolismo , GMP Cíclico/metabolismo , Proteínas Fúngicas/metabolismo , Guanilato Ciclase/metabolismo , Rodopsina/metabolismo , Espectroscopia de Infravermelho com Transformada de Fourier
2.
Nat Commun ; 11(1): 5682, 2020 11 10.
Artigo em Inglês | MEDLINE | ID: mdl-33173168

RESUMO

The Rhizoclosmatium globosum genome encodes three rhodopsin-guanylyl cyclases (RGCs), which are predicted to facilitate visual orientation of the fungal zoospores. Here, we show that RGC1 and RGC2 function as light-activated cyclases only upon heterodimerization with RGC3 (NeoR). RGC1/2 utilize conventional green or blue-light-sensitive rhodopsins (λmax = 550 and 480 nm, respectively), with short-lived signaling states, responsible for light-activation of the enzyme. The bistable NeoR is photoswitchable between a near-infrared-sensitive (NIR, λmax = 690 nm) highly fluorescent state (QF = 0.2) and a UV-sensitive non-fluorescent state, thereby modulating the activity by NIR pre-illumination. No other rhodopsin has been reported so far to be functional as a heterooligomer, or as having such a long wavelength absorption or high fluorescence yield. Site-specific mutagenesis and hybrid quantum mechanics/molecular mechanics simulations support the idea that the unusual photochemical properties result from the rigidity of the retinal chromophore and a unique counterion triad composed of two glutamic and one aspartic acids. These findings substantially expand our understanding of the natural potential and limitations of spectral tuning in rhodopsin photoreceptors.


Assuntos
Quitridiomicetos/genética , Rodopsina , Biologia Computacional , Fluorescência , Corantes Fluorescentes/química , Corantes Fluorescentes/isolamento & purificação , Genes Fúngicos , Genoma Fúngico , Mutagênese Sítio-Dirigida , Processos Fotoquímicos , Células Fotorreceptoras/fisiologia , Rodopsina/biossíntese , Rodopsina/química , Rodopsina/genética
3.
J Am Chem Soc ; 142(26): 11464-11473, 2020 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-32475117

RESUMO

UV-absorbing rhodopsins are essential for UV vision and sensing in all kingdoms of life. Unlike the well-known visible-absorbing rhodopsins, which bind a protonated retinal Schiff base for light absorption, UV-absorbing rhodopsins bind an unprotonated retinal Schiff base. Thus far, the photoreaction dynamics and mechanisms of UV-absorbing rhodopsins have remained essentially unknown. Here, we report the complete excited- and ground-state dynamics of the UV form of histidine kinase rhodopsin 1 (HKR1) from eukaryotic algae, using femtosecond stimulated Raman spectroscopy (FSRS) and transient absorption spectroscopy, covering time scales from femtoseconds to milliseconds. We found that energy-level ordering is inverted with respect to visible-absorbing rhodopsins, with an optically forbidden low-lying S1 excited state that has Ag- symmetry and a higher-lying UV-absorbing S2 state of Bu+ symmetry. UV-photoexcitation to the S2 state elicits a unique dual-isomerization reaction: first, C13═C14 cis-trans isomerization occurs during S2-S1 evolution in <100 fs. This very fast reaction features the remarkable property that the newly formed isomer appears in the excited state rather than in the ground state. Second, C15═N16 anti-syn isomerization occurs on the S1-S0 evolution to the ground state in 4.8 ps. We detected two ground-state unprotonated retinal photoproducts, 13-trans/15-anti (all-trans) and 13-cis/15-syn, after relaxation to the ground state. These isomers become protonated in 58 µs and 3.2 ms, respectively, resulting in formation of the blue-absorbing form of HKR1. Our results constitute a benchmark of UV-induced photochemistry of animal and microbial rhodopsins.

4.
Nat Commun ; 10(1): 3315, 2019 07 25.
Artigo em Inglês | MEDLINE | ID: mdl-31346176

RESUMO

Channelrhodopsins (ChRs) are algal light-gated ion channels widely used as optogenetic tools for manipulating neuronal activity. ChRs desensitize under continuous bright-light illumination, resulting in a significant decline of photocurrents. Here we describe a metagenomically identified family of phylogenetically distinct anion-conducting ChRs (designated MerMAIDs). MerMAIDs almost completely desensitize during continuous illumination due to accumulation of a late non-conducting photointermediate that disrupts the ion permeation pathway. MerMAID desensitization can be fully explained by a single photocycle in which a long-lived desensitized state follows the short-lived conducting state. A conserved cysteine is the critical factor in desensitization, as its mutation results in recovery of large stationary photocurrents. The rapid desensitization of MerMAIDs enables their use as optogenetic silencers for transient suppression of individual action potentials without affecting subsequent spiking during continuous illumination. Our results could facilitate the development of optogenetic tools from metagenomic databases and enhance general understanding of ChR function.


Assuntos
Ânions/metabolismo , Bactérias/genética , Channelrhodopsins/genética , Família Multigênica , Vírus/genética , Animais , Bactérias/classificação , Bactérias/isolamento & purificação , Bactérias/metabolismo , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Channelrhodopsins/química , Channelrhodopsins/metabolismo , Humanos , Cinética , Luz , Metagenoma , Neurônios/metabolismo , Optogenética , Filogenia , Água do Mar/microbiologia , Água do Mar/virologia , Proteínas Virais/genética , Proteínas Virais/metabolismo , Vírus/classificação , Vírus/isolamento & purificação , Vírus/metabolismo
5.
Curr Opin Struct Biol ; 57: 118-126, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-30954887

RESUMO

Enzymerhodopsins are a recently discovered class of natural rhodopsin-based photoreceptors with light-regulated enzyme activity. Currently, three different types of these fusion proteins with an N-terminal type-1 rhodopsin and a C-terminal enzyme domain have been identified, but their physiological relevance is mostly unknown. Among these, histidine kinase rhodopsins (HKR) are photo-regulated two-component-like signaling systems that trigger a phosphorylation cascade, whereas rhodopsin phosphodiesterase (RhoPDE) or rhodopsin guanylyl cyclase (RhGC) show either light-activated hydrolysis or production of cyclic nucleotides. RhGC, the best characterized enzymerhodopsin, is involved in the phototaxis of fungal zoospores and allows for optically controlled production of cyclic nucleotides in different cell-types. These photoreceptors have great optogenetic potential and possess several advantages over the hitherto existing tools to manipulate cyclic-nucleotide dynamics in living cells.


Assuntos
Biocatálise , Enzimas/metabolismo , Optogenética/métodos , Rodopsina/metabolismo , Rodopsina/química
6.
Nano Lett ; 19(5): 3104-3114, 2019 05 08.
Artigo em Inglês | MEDLINE | ID: mdl-30950626

RESUMO

Photosensitive proteins embedded in the cell membrane (about 5 nm thickness) act as photoactivated proton pumps, ion gates, enzymes, or more generally, as initiators of stimuli for the cell activity. They are composed of a protein backbone and a covalently bound cofactor (e.g. the retinal chromophore in bacteriorhodopsin (BR), channelrhodopsin, and other opsins). The light-induced conformational changes of both the cofactor and the protein are at the basis of the physiological functions of photosensitive proteins. Despite the dramatic development of microscopy techniques, investigating conformational changes of proteins at the membrane monolayer level is still a big challenge. Techniques based on atomic force microscopy (AFM) can detect electric currents through protein monolayers and even molecular binding forces in single-protein molecules but not the conformational changes. For the latter, Fourier-transform infrared spectroscopy (FTIR) using difference-spectroscopy mode is typically employed, but it is performed on macroscopic liquid suspensions or thick films containing large amounts of purified photosensitive proteins. In this work, we develop AFM-assisted, tip-enhanced infrared difference-nanospectroscopy to investigate light-induced conformational changes of the bacteriorhodopsin mutant D96N in single submicrometric native purple membrane patches. We obtain a significant improvement compared with the signal-to-noise ratio of standard IR nanospectroscopy techniques by exploiting the field enhancement in the plasmonic nanogap that forms between a gold-coated AFM probe tip and an ultraflat gold surface, as further supported by electromagnetic and thermal simulations. IR difference-spectra in the 1450-1800 cm-1 range are recorded from individual patches as thin as 10 nm, with a diameter of less than 500 nm, well beyond the diffraction limit for FTIR microspectroscopy. We find clear spectroscopic evidence of a branching of the photocycle for BR molecules in direct contact with the gold surfaces, with equal amounts of proteins either following the standard proton-pump photocycle or being trapped in an intermediate state not directly contributing to light-induced proton transport. Our results are particularly relevant for BR-based optoelectronic and energy-harvesting devices, where BR molecular monolayers are put in contact with metal surfaces, and, more generally, for AFM-based IR spectroscopy studies of conformational changes of proteins embedded in intrinsically heterogeneous native cell membranes.


Assuntos
Bacteriorodopsinas/ultraestrutura , Proteínas de Membrana/ultraestrutura , Proteínas Mutantes/ultraestrutura , Bombas de Próton/ultraestrutura , Bacteriorodopsinas/química , Bacteriorodopsinas/genética , Campos Eletromagnéticos , Transporte de Íons/genética , Proteínas de Membrana/química , Microscopia de Força Atômica , Proteínas Mutantes/química , Proteínas Mutantes/genética , Nanotecnologia/métodos , Conformação Proteica , Bombas de Próton/química , Membrana Purpúrea/química , Membrana Purpúrea/ultraestrutura , Espectroscopia de Infravermelho com Transformada de Fourier
7.
Nat Commun ; 9(1): 2046, 2018 05 24.
Artigo em Inglês | MEDLINE | ID: mdl-29799525

RESUMO

The cyclic nucleotides cAMP and cGMP are important second messengers that orchestrate fundamental cellular responses. Here, we present the characterization of the rhodopsin-guanylyl cyclase from Catenaria anguillulae (CaRhGC), which produces cGMP in response to green light with a light to dark activity ratio >1000. After light excitation the putative signaling state forms with τ = 31 ms and decays with τ = 570 ms. Mutations (up to 6) within the nucleotide binding site generate rhodopsin-adenylyl cyclases (CaRhACs) of which the double mutated YFP-CaRhAC (E497K/C566D) is the most suitable for rapid cAMP production in neurons. Furthermore, the crystal structure of the ligand-bound AC domain (2.25 Å) reveals detailed information about the nucleotide binding mode within this recently discovered class of enzyme rhodopsin. Both YFP-CaRhGC and YFP-CaRhAC are favorable optogenetic tools for non-invasive, cell-selective, and spatio-temporally precise modulation of cAMP/cGMP with light.


Assuntos
Adenilil Ciclases/química , Blastocladiomycota/enzimologia , AMP Cíclico/química , GMP Cíclico/química , Proteínas Fúngicas/química , Guanilato Ciclase/química , Rodopsina/química , Adenilil Ciclases/genética , Adenilil Ciclases/metabolismo , Animais , Sítios de Ligação , Blastocladiomycota/química , Blastocladiomycota/genética , Cristalização , AMP Cíclico/metabolismo , GMP Cíclico/metabolismo , Proteínas Fúngicas/metabolismo , Guanilato Ciclase/genética , Guanilato Ciclase/metabolismo , Modelos Moleculares , Ligação Proteica , Domínios Proteicos , Ratos , Rodopsina/metabolismo
8.
Phys Chem Chem Phys ; 19(45): 30402-30409, 2017 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-29125160

RESUMO

Anion channelrhodopsins (ACRs) are of great interest due to their ability to inhibit electrical signaling in optogenetic experiments. The photochemistry of ACRs is currently poorly understood and an improved understanding would be beneficial for rational design of ACRs with modified properties. Activation/deactivation of ACRs involves a series of photoreactions ranging from femtoseconds to seconds, thus real-time observation is essential to comprehend the full complexity of the photochemical processes. Here we investigate the photocycle of an ACR from Proteomonas sulcata (PsACR1), which is valuable for optogenetic applications due to the red-shifted absorption and action spectra compared to the prototype ACRs from Guillardia theta: GtACR1 and GtACR2, and the fast channel closing properties. From femto-to-submillisecond transient absorption spectroscopy, flash photolysis, and point mutations of acidic residues near the retinal Schiff base (RSB), E64, and D230, we found that the photoisomerization occurs in ∼500 fs independent of the protonation state of E64. Notably, E64 is involved in the rearrangement of the hydrogen-bond network near the RSB after photoisomerization. Furthermore, we suggest that E64 works as a primary proton acceptor during deprotonation of the RSB as has been proposed for GtACR1. Our findings allow for a deeper understanding of the photochemistry on the activation/deactivation of ACRs.

9.
J Biol Chem ; 291(8): 4121-7, 2016 Feb 19.
Artigo em Inglês | MEDLINE | ID: mdl-26740624

RESUMO

Chloride conducting channelrhodopsins (ChloCs) are new members of the optogenetic toolbox that enable neuronal inhibition in target cells. Originally, ChloCs have been engineered from cation conducting channelrhodopsins (ChRs), and later identified in a cryptophyte alga genome. We noticed that the sequence of a previously described Proteomonas sulcata ChR (PsChR1) was highly homologous to the naturally occurring and previously reported ChloCs GtACR1/2, but was not recognized as an anion conducting channel. Based on electrophysiological measurements obtained under various ionic conditions, we concluded that the PsChR1 photocurrent at physiological conditions is strongly inward rectifying and predominantly carried by chloride. The maximum activation was noted at excitation with light of 540 nm. An initial spectroscopic characterization of purified protein revealed that the photocycle and the transport mechanism of PsChR1 differ significantly from cation conducting ChRs. Hence, we concluded that PsChR1 is an anion conducting ChR, now renamed PsACR1, with a red-shifted absorption suited for multicolor optogenetic experiments in combination with blue light absorbing cation conducting ChRs.


Assuntos
Canais de Cloreto/química , Criptófitas/química , Luz , Rodopsina/química , Canais de Cloreto/genética , Canais de Cloreto/metabolismo , Criptófitas/genética , Criptófitas/metabolismo , Transporte de Íons/fisiologia , Rodopsina/genética , Rodopsina/metabolismo
10.
J Biol Chem ; 288(31): 22607-20, 2013 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-23766513

RESUMO

The oxygen-evolving complex (OEC) in the membrane-bound protein complex photosystem II (PSII) catalyzes the water oxidation reaction that takes place in oxygenic photosynthetic organisms. We investigated the structural changes of the Mn4CaO5 cluster in the OEC during the S state transitions using x-ray absorption spectroscopy (XAS). Overall structural changes of the Mn4CaO5 cluster, based on the manganese ligand and Mn-Mn distances obtained from this study, were incorporated into the geometry of the Mn4CaO5 cluster in the OEC obtained from a polarized XAS model and the 1.9-Å high resolution crystal structure. Additionally, we compared the S1 state XAS of the dimeric and monomeric form of PSII from Thermosynechococcus elongatus and spinach PSII. Although the basic structures of the OEC are the same for T. elongatus PSII and spinach PSII, minor electronic structural differences that affect the manganese K-edge XAS between T. elongatus PSII and spinach PSII are found and may originate from differences in the second sphere ligand atom geometry.


Assuntos
Oxigênio/química , Complexo de Proteína do Fotossistema II/química , Catálise
11.
J Biol Chem ; 286(18): 15964-72, 2011 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-21367867

RESUMO

Herbicides that target photosystem II (PSII) compete with the native electron acceptor plastoquinone for binding at the Q(B) site in the D1 subunit and thus block the electron transfer from Q(A) to Q(B). Here, we present the first crystal structure of PSII with a bound herbicide at a resolution of 3.2 Å. The crystallized PSII core complexes were isolated from the thermophilic cyanobacterium Thermosynechococcus elongatus. The used herbicide terbutryn is found to bind via at least two hydrogen bonds to the Q(B) site similar to photosynthetic reaction centers in anoxygenic purple bacteria. Herbicide binding to PSII is also discussed regarding the influence on the redox potential of Q(A), which is known to affect photoinhibition. We further identified a second and novel chloride position close to the water-oxidizing complex and in the vicinity of the chloride ion reported earlier (Guskov, A., Kern, J., Gabdulkhakov, A., Broser, M., Zouni, A., and Saenger, W. (2009) Nat. Struct. Mol. Biol. 16, 334-342). This discovery is discussed in the context of proton transfer to the lumen.


Assuntos
Cianobactérias/enzimologia , Herbicidas/química , Complexo de Proteína do Fotossistema II/química , Triazinas/química , Cristalografia por Raios X , Herbicidas/farmacologia , Complexo de Proteína do Fotossistema II/antagonistas & inibidores , Complexo de Proteína do Fotossistema II/metabolismo , Estrutura Quaternária de Proteína , Relação Estrutura-Atividade , Triazinas/farmacologia
12.
J Biol Chem ; 285(34): 26255-62, 2010 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-20558739

RESUMO

The membrane-embedded photosystem II core complex (PSIIcc) uses light energy to oxidize water in photosynthesis. Information about the spatial structure of PSIIcc obtained from x-ray crystallography was so far derived from homodimeric PSIIcc of thermophilic cyanobacteria. Here, we report the first crystallization and structural analysis of the monomeric form of PSIIcc with high oxygen evolution capacity, isolated from Thermosynechococcus elongatus. The crystals belong to the space group C222(1), contain one monomer per asymmetric unit, and diffract to a resolution of 3.6 A. The x-ray diffraction pattern of the PSIIcc-monomer crystals exhibit less anisotropy (dependence of resolution on crystal orientation) compared with crystals of dimeric PSIIcc, and the packing of the molecules within the unit cell is different. In the monomer, 19 protein subunits, 35 chlorophylls, two pheophytins, the non-heme iron, the primary plastoquinone Q(A), two heme groups, 11 beta-carotenes, 22 lipids, seven detergent molecules, and the Mn(4)Ca cluster of the water oxidizing complex could be assigned analogous to the dimer. Based on the new structural information, the roles of lipids and protein subunits in dimer formation of PSIIcc are discussed. Due to the lack of non-crystallographic symmetry and the orientation of the membrane normal of PSIIcc perpendicular ( approximately 87 degrees ) to the crystallographic b-axis, further information about the structure of the Mn(4)Ca cluster is expected to become available from orientation-dependent spectroscopy on this new crystal form.


Assuntos
Cianobactérias/química , Complexo de Proteína do Fotossistema II/química , Anisotropia , Cálcio , Cristalografia por Raios X , Lipídeos , Substâncias Macromoleculares/química , Manganês , Multimerização Proteica , Subunidades Proteicas
13.
Chemphyschem ; 11(6): 1160-71, 2010 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-20352642

RESUMO

The photosynthetic oxygen-evolving photosystem II (PSII) is the only known biochemical system that is able to oxidize water molecules and thereby generates almost all oxygen in the Earth's atmosphere. The elucidation of the structural and mechanistic aspects of PSII keeps scientists all over the world engaged since several decades. In this Minireview, we outline the progress in understanding PSII based on the most recent crystal structure at 2.9 A resolution. A likely position of the chloride ion, which is known to be required for the fast turnover of water oxidation, could be determined in native PSII and is compared with work on bromide and iodide substituted PSII. Moreover, eleven new integral lipids could be assigned, emphasizing the importance of lipids for the perfect function of PSII. A third plastoquinone molecule (Q(C)) and a second quinone transfer channel are revealed, making it possible to consider different mechanisms for the exchange of plastoquinone/plastoquinol molecules. In addition, possible transport channels for water, dioxygen and protons are identified.


Assuntos
Complexo de Proteína do Fotossistema II/química , Sítios de Ligação , Cristalografia por Raios X , Cianobactérias/enzimologia , Lipídeos/química , Oxirredução , Complexo de Proteína do Fotossistema II/metabolismo , Plastoquinona/química , Conformação Proteica , Água/química
14.
Structure ; 17(9): 1223-34, 2009 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-19748343

RESUMO

Using the 2.9 A resolution structure of the membrane-intrinsic protein-cofactor complex photosystem II (PSII) from the cyanobacterium Thermosynechococcus elongatus, we calculated and characterized nine possible substrate/product channels leading to/away from the Mn(4)Ca cluster, where water is oxidized to dioxygen, protons, and electrons. Five narrow channels could function in proton transport, assuming that no large structural changes are associated with water oxidation. Four wider channels could serve to supply water to or remove oxygen from the Mn(4)Ca cluster. One of them might be regulated by conformational changes of Lys134 in subunit PsbU. Data analyses of Kr derivatized crystals and complexes with dimethyl sulfoxide (DMSO) confirm the accessibility of the proposed dioxygen channels to other molecules. Results from Xe derivatization suggest that the lipid clusters within PSII could serve as a drain for oxygen because of their predominant hydrophobic character and mediate dioxygen release from the lumen.


Assuntos
Dimetil Sulfóxido/química , Manganês/química , Sondas Moleculares , Gases Nobres/química , Complexo de Proteína do Fotossistema II/química , Cristalização , Modelos Moleculares , Oxigênio/química
15.
Phys Chem Chem Phys ; 11(31): 6715-26, 2009 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-19639145

RESUMO

Pulsed electron nuclear double resonance (ENDOR) spectroscopy at Q- and W-band frequencies was applied to single crystals of photosystem II from Th. elongatus. W-Band (1)H-ENDOR on the dark-stable radical state Y of the redox-active tyrosine residue Y(D) yields a complete mapping of the electronic structure of this amino acid radical in terms of an assignment of all hyperfine coupling tensors of the protons covalently bound to the side chain. This study can serve as a model case for the potential of high-field/high-frequency ENDOR on protein single crystals for obtaining highly resolved electronic structure information. Q-band (55)Mn-ENDOR was applied to the S(2) oxidation state of the water-splitting complex in photosystem II single crystals. Irrespective of the difficulties arising from the extremely broad electron paramagnetic resonance (EPR) spectroscopy ( approximately 200 mT) and ENDOR ( approximately 100 MHz) spectra a tentative assignment of the Mn ion in the formal oxidation state III to a Mn position in the structural model of PSII is possible on the basis of the ENDOR data.


Assuntos
Espectroscopia de Ressonância de Spin Eletrônica/métodos , Complexo de Proteína do Fotossistema II/química , Tirosina/análogos & derivados , Água/química , Cristalografia , Cianobactérias/enzimologia , Manganês/química , Modelos Moleculares , Tirosina/química
16.
Nat Struct Mol Biol ; 16(3): 334-42, 2009 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-19219048

RESUMO

Photosystem II (PSII) is a large homodimeric protein-cofactor complex located in the photosynthetic thylakoid membrane that acts as light-driven water:plastoquinone oxidoreductase. The crystal structure of PSII from Thermosynechococcus elongatus at 2.9-A resolution allowed the unambiguous assignment of all 20 protein subunits and complete modeling of all 35 chlorophyll a molecules and 12 carotenoid molecules, 25 integral lipids and 1 chloride ion per monomer. The presence of a third plastoquinone Q(C) and a second plastoquinone-transfer channel, which were not observed before, suggests mechanisms for plastoquinol-plastoquinone exchange, and we calculated other possible water or dioxygen and proton channels. Putative oxygen positions obtained from a Xenon derivative indicate a role for lipids in oxygen diffusion to the cytoplasmic side of PSII. The chloride position suggests a role in proton-transfer reactions because it is bound through a putative water molecule to the Mn(4)Ca cluster at a distance of 6.5 A and is close to two possible proton channels.


Assuntos
Proteínas de Bactérias/química , Cianobactérias/química , Complexo de Proteína do Fotossistema II/química , Estrutura Quaternária de Proteína , Sítios de Ligação , Cloretos/química , Cristalografia por Raios X , Lipídeos/química , Modelos Moleculares , Subunidades Proteicas/química , Quinonas/química
17.
Biol Chem ; 389(5): 609-17, 2008 May.
Artigo em Inglês | MEDLINE | ID: mdl-18953728

RESUMO

In the cyanobacterium Thermosynechococcus elongatus BP-1, living in hot springs, the light environment directly regulates expression of genes that encode key components of the photosynthetic multi-subunit protein-pigment complex photosystem II (PSII). Light is not only essential as an energy source to power photosynthesis, but leads to formation of aggressive radicals which induce severe damage of protein subunits and organic cofactors. Photosynthetic organisms develop several protection mechanisms against this photo-damage, such as the differential expression of genes coding for the reaction center subunit D1 in PSlI. Testing the expression of the three different genes (psbAI, psbAII, psbAIII) coding for D1 in T. elongatus under culture conditions used for preparing the material used in crystallization of PSII showed that under these conditions only subunit PsbA1 is present. However, exposure to high-light intensity induced partial replacement of PsbA1 with PsbA3. Modeling of the variant amino acids of the three different D1 copies in the 3.0 A resolution crystal structure of PSII revealed that most of them are in the direct vicinity to redox-active cofactors of the electron transfer chain. Possible structural and mechanistic consequences for electron transfer are discussed.


Assuntos
Cianobactérias/química , Cianobactérias/genética , Complexo de Proteína do Fotossistema II/química , Sequência de Aminoácidos , Grupo dos Citocromos b/genética , Grupo dos Citocromos c/genética , Bases de Dados Genéticas , Transporte de Elétrons/fisiologia , Genes Bacterianos , Modelos Moleculares , Dados de Sequência Molecular , Complexo de Proteína do Fotossistema II/genética , Ligação Proteica , Quinonas/química , Reação em Cadeia da Polimerase Via Transcriptase Reversa
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...