| 1. |
- Su, Ji-Hu, et al.
(författare)
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The electronic structures of the S(2) states of the oxygen evolving complexes of photosystem II in plants and cyanobacteria in the presence and absence of methanol
- 2011
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Ingår i: Biochimica et Biophysica Acta. - Amsterdam : Elsevier. - 0006-3002 .- 1878-2434 .- 0005-2728 .- 1879-2650. ; 1807:7, s. 829-840
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Tidskriftsartikel (refereegranskat)abstract
- The electronic properties of the Mn(4)O(x)Ca cluster in the S(2) state of the oxygen evolving complex (OEC) were studied using X- and Q-band EPR and Q-band (55)Mn-ENDOR using photosystem II preparations isolated from the thermophilic cyanobacterium T. elongatus and higher plants (spinach). The data presented here show that there is very little difference between the two species. Specifically it is shown that: (i) only small changes are seen in the fitted isotropic hyperfine values, suggesting that there is no significant difference in the overall spin distribution (electronic coupling scheme) between the two species; (ii) the inferred fine-structure tensor of the only Mn(III) ion in the cluster is of the same magnitude and geometry for both species types, suggesting that the Mn(III) ion has the same coordination sphere in both sample preparations; and (iii) the data from both species are consistent with only one structural model available in the literature, namely the Siegbahn structure [Siegbahn, P. E. M. Accounts Chem. Res.2009, 42, 1871-1880, Pantazis, D. A. et al., Phys. Chem. Chem. Phys.2009, 11, 6788-6798]. These measurements were made in the presence of methanol because it confers favorable magnetic relaxation properties to the cluster that facilitate pulse-EPR techniques. In the absence of methanol the separation of the ground state and the first excited state of the spin system is smaller. For cyanobacteria this effect is minor but in plant PS II it leads to a break-down of the S(T)=½ spin model of the S(2) state. This suggests that the methanol-OEC interaction is species dependent. It is proposed that the effect of small organic solvents on the electronic structure of the cluster is to change the coupling between the outer Mn (Mn(A)) and the other three Mn ions that form the trimeric part of the cluster (Mn(B), Mn(C), Mn(D)), by perturbing the linking bis-μ-oxo bridge. The flexibility of this bridging unit is discussed with regard to the mechanism of O-O bond formation.
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| 2. |
- Ames, William, et al.
(författare)
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Theoretical Evaluation of Structural Models of the S(2) State in the Oxygen Evolving Complex of Photosystem II : Protonation States and Magnetic Interactions
- 2011
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 133:49, s. 19743-19757
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Tidskriftsartikel (refereegranskat)abstract
- Protonation states of water ligands and oxo bridges are intimately involved in tuning the electronic structures and oxidation potentials of the oxygen evolving complex (OEC) in Photosystem II, steering the mechanistic pathway, which involves at least five redox state intermediates S(n) (n = 0-4) resulting in the oxidation of water to molecular oxygen. Although protons are practically invisible in protein crystallography, their effects on the electronic structure and magnetic properties of metal active sites can be probed using spectroscopy. With the twin purpose of aiding the interpretation of the complex electron paramagnetic resonance (EPR) spectroscopic data of the OEC and of improving the view of the cluster at the atomic level, a complete set of protonation configurations for the S(2) state of the OEC were investigated, and their distinctive effects on magnetic properties of the cluster were evaluated. The most recent X-ray structure of Photosystem II at 1.9 Å resolution was used and refined to obtain the optimum structure for the Mn(4)O(5)Ca core within the protein pocket. Employing this model, a set of 26 structures was constructed that tested various protonation scenarios of the water ligands and oxo bridges. Our results suggest that one of the two water molecules that are proposed to coordinate the outer Mn ion (Mn(A)) of the cluster is deprotonated in the S(2) state, as this leads to optimal experimental agreement, reproducing the correct ground state spin multiplicity (S = 1/2), spin expectation values, and EXAFS-derived metal-metal distances. Deprotonation of Ca(2+)-bound water molecules is strongly disfavored in the S(2) state, but dissociation of one of the two water ligands appears to be facile. The computed isotropic hyperfine couplings presented here allow distinctions between models to be made and call into question the assumption that the largest coupling is always attributable to Mn(III). The present results impose limits for the total charge and the proton configuration of the OEC in the S(2) state, with implications for the cascade of events in the Kok cycle and for the water splitting mechanism.
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| 3. |
- Cox, Nicholas, et al.
(författare)
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Electronic Structure of a Weakly Antiferromagnetically Coupled Mn(II)Mn(III) Model Relevant to Manganese Proteins : A Combined EPR, (55)Mn-ENDOR, and DFT Study
- 2011
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Ingår i: Inorganic Chemistry. - : American Chemical Society. - 0020-1669 .- 1520-510X. ; 50:17, s. 8238-8251
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Tidskriftsartikel (refereegranskat)abstract
- An analysis of the electronic structure of the [Mn(II)Mn(III)(μ-OH)-(μ-piv)(2)(Me(3)tacn)(2)](ClO(4))(2) (PivOH) complex is reported. It displays features that include: (i) a ground 1/2 spin state; (ii) a small exchange (J) coupling between the two Mn ions; (iii) a mono-μ-hydroxo bridge, bis-μ-carboxylato motif; and (iv) a strongly coupled, terminally bound N ligand to the Mn(III). All of these features are observed in structural models of the oxygen evolving complex (OEC). Multifrequency electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) measurements were performed on this complex, and the resultant spectra simulated using the Spin Hamiltonian formalism. The strong field dependence of the (55)Mn-ENDOR constrains the (55)Mn hyperfine tensors such that a unique solution for the electronic structure can be deduced. Large hyperfine anisotropy is required to reproduce the EPR/ENDOR spectra for both the Mn(II) and Mn(III) ions. The large effective hyperfine tensor anisotropy of the Mn(II), a d(5) ion which usually exhibits small anisotropy, is interpreted within a formalism in which the fine structure tensor of the Mn(III) ion strongly perturbs the zero-field energy levels of the Mn(II)Mn(III) complex. An estimate of the fine structure parameter (d) for the Mn(III) of -4 cm(-1) was made, by assuming the intrinsic anisotropy of the Mn(II) ion is small. The magnitude of the fine structure and intrinsic (onsite) hyperfine tensor of the Mn(III) is consistent with the known coordination environment of the Mn(III) ion as seen from its crystal structure. Broken symmetry density functional theory (DFT) calculations were performed on the crystal structure geometry. DFT values for both the isotropic and the anisotropic components of the onsite (intrinsic) hyperfine tensors match those inferred from the EPR/ENDOR simulations described above, to within 5%. This study demonstrates that DFT calculations provide reliable estimates for spectroscopic observables of mixed valence Mn complexes, even in the limit where the description of a well isolated S = 1/2 ground state begins to break down.
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| 4. |
- Cox, Nicholas, et al.
(författare)
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Electronic Structure of a Weakly Antiferromagnetically Coupled MnIIMnIII Model Relevant to Manganese Proteins : A Combined EPR, 55Mn-ENDOR, and DFT Study
- 2011
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Ingår i: Inorganic Chemistry. - : AMER CHEMICAL SOC. - 0020-1669 .- 1520-510X. ; 50:17, s. 8238-8251
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Tidskriftsartikel (refereegranskat)abstract
- An analysis of the electronic structure of the [(MnMnIII)-Mn-II(mu-OH)-(mu-piv)(2)(Me(3)tacn)(2)] (ClO4)(2) (PivOH) complex is reported. It displays features that include: (i) a ground 1/2 spin state; (ii) a small exchange (J) coupling between the two Mn ions; (iii) a mono-mu-hydroxo bridge, bis-mu-carboxylato motif; and (iv) a strongly coupled, terminally bound N ligand to the Mn-III. All of these features are observed in structural models of the oxygen evolving complex (OEC). Multifrequency electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) measurements were performed on this complex, and the resultant spectra simulated using the Spin Hamiltonian formalism. The strong field dependence of the Mn-55-ENDOR constrains the Mn-55 hyperfine tensors such that a unique solution for the electronic structure can be deduced. Large hyperfine anisotropy is required to reproduce the EPR/ENDOR spectra for both the Mn-II and Mn-III ions. The large effective hyperfine tensor anisotropy of the Mn-II, a d(5) ion which usually exhibits small anisotropy, is interpreted within a formalism in which the fine structure tensor of the Mn-III ion strongly perturbs the zero-field energy levels of the (MnMnIII)-Mn-II complex. An estimate of the fine structure parameter (d) for the Mn-III of -4 cm(-1) was made, by assuming the intrinsic anisotropy of the Mn-II ion is small. The magnitude of the fine structure and intrinsic (onsite) hyperfine tensor of the Mn-III is consistent with the known coordination environment of the Mn-III ion as seen from its crystal structure. Broken symmetry density functional theory (DFT) calculations were performed on the crystal structure geometry. DFT values for both the isotropic and the anisotropic components of the onsite (intrinsic) hyperfine tensors match those inferred from the EPR/ENDOR simulations described above, to within 5%. This study demonstrates that DFT calculations provide reliable estimates for spectroscopic observables of mixed valence Mn complexes, even in the limit where the description of a well isolated S = 1/2 ground state begins to break down.
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| 5. |
- Kuppler, Jonas, et al.
(författare)
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Global gradients in intraspecific variation in vegetative and floral traits are partially associated with climate and species richness
- 2020
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Ingår i: Global Ecology and Biogeography. - : Wiley. - 1466-822X .- 1466-8238. ; 29:6, s. 992-1007
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Tidskriftsartikel (refereegranskat)abstract
- AimIntraspecific trait variation (ITV) within natural plant communities can be large, influencing local ecological processes and dynamics. Here, we shed light on how ITV in vegetative and floral traits responds to large‐scale abiotic and biotic gradients (i.e., climate and species richness). Specifically, we tested whether associations of ITV with temperature, precipitation and species richness were consistent with any of four hypotheses relating to stress tolerance and competition. Furthermore, we estimated the degree of correlation between ITV in vegetative and floral traits and how they vary along the gradients.LocationGlobal.Time period1975–2016.Major taxa studiedHerbaceous and woody plants.MethodsWe compiled a dataset of 18,401 measurements of the absolute extent of ITV (measured as the coefficient of variation) in nine vegetative and seven floral traits from 2,822 herbaceous and woody species at 2,372 locations.ResultsLarge‐scale associations between ITV and climate were trait specific and more prominent for vegetative traits, especially leaf morphology, than for floral traits. The ITV showed pronounced associations with climate, with lower ITV values in colder areas and higher values in drier areas. The associations of ITV with species richness were inconsistent across traits. Species‐specific associations across gradients were often idiosyncratic, and covariation in ITV was weaker between vegetative and floral traits than within the two trait groups.Main conclusionsOur results show that, depending on the traits considered, ITV either increased or decreased with climate stress and species richness, suggesting that both factors can constrain or enhance ITV, which might foster plant‐population persistence in stressful conditions. Given the species‐specific responses and covariation in ITV, associations can be hard to predict for traits and species not yet studied. We conclude that consideration of ITV can improve our understanding of how plants cope with stressful conditions and environmental change across spatial and biological scales.
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| 6. |
- Myers, William K., et al.
(författare)
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Double Electron-Electron Resonance Probes Ca2+-Induced Conformational Changes and Dimerization of Recoverin
- 2013
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 52:34, s. 5800-5808
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Tidskriftsartikel (refereegranskat)abstract
- Recoverin a member of the neuronal calcium sensor (NCS) branch of the calmodulin superfamily, is expressed in retinal photoreceptor cells and serves as a calcium sensor in vision. Ca2+-induced conformational changes in recoverin cause extrusion of its covalently attached myristate (termed Ca2+-myristoyl switch) that promotes translocation of recoverin to disk membranes during phototransduction in retinal rod cells. Here we report double electron electron resonance (DEER) experiments on recoverin that probe Ca2+-induced changes in distance as measured by the dipolar coupling between spin-labels strategically positioned at engineered cysteine residues on the protein surface. The DEER distance between nitroxide spin-labels attached at C39 and N120C is 2.5 +/- 0.1 nm for Ca2+-free recoverin and 3.7 +/- 0.1 nm for Ca2+-bound recoverin. An additional DEER distance (5-6 nm) observed for Ca2+-bound recoverin may represent an intermolecular distance between C39 and N120. N-15 NMR relaxation analysis and CW-EPR experiments both confirm that Ca2+-bound recoverin forms a dimer at protein concentrations above 100 mu M, whereas Ca2+-free recoverin is monomeric We propose that Ca2+-induced dimerization of recoverin at the disk membrane surface may play a role in regulating Ca2+-dependent phosphorylation of dimeric rhodopsin. The DEER approach will be useful for elucidating dimeric structures of NCS proteins in general for which Ca2+-induced dimerization is functionally important but not well understood.
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| 7. |
- Navarro, Montserrat Perez, et al.
(författare)
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Ammonia binding to the oxygen-evolving complex of photosystem II identifies the solvent-exchangeable oxygen bridge (µ-oxo) of the manganese tetramer
- 2013
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 110:39, s. 15561-15566
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Tidskriftsartikel (refereegranskat)abstract
- The assignment of the two substrate water sites of the tetramanganese penta-oxygen calcium (Mn4O5Ca) cluster of photosystem II is essential for the elucidation of the mechanism of biological O-O bond formation and the subsequent design of bio-inspired water-splitting catalysts. We recently demonstrated using pulsed EPR spectroscopy that one of the five oxygen bridges (mu-oxo) exchanges unusually rapidly with bulk water and is thus a likely candidate for one of the substrates. Ammonia, a water analog, was previously shown to bind to the Mn4O5Ca cluster, potentially displacing a water/substrate ligand [Britt RD, et al. (1989) J Am Chem Soc 111(10):3522-3532]. Here we show by a combination of EPR and time-resolved membrane inlet mass spectrometry that the binding of ammonia perturbs the exchangeable mu-oxo bridge without drastically altering the binding/exchange kinetics of the two substrates. In combination with broken-symmetry density functional theory, our results show that (i) the exchangable mu-oxo bridge is O5 {using the labeling of the current crystal structure [Umena Y, et al. (2011) Nature 473(7345):55-60]}; (ii) ammonia displaces a water ligand to the outer manganese (Mn-A4-W1); and (iii) as W1 is trans to O5, ammonia binding elongates the Mn-A4-O5 bond, leading to the perturbation of the mu-oxo bridge resonance and to a small change in the water exchange rates. These experimental results support O-O bond formation between O5 and possibly an oxyl radical as proposed by Siegbahn and exclude W1 as the second substrate water.
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| 8. |
- Rapatskiy, Leonid, et al.
(författare)
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Characterization of Oxygen Bridged Manganese Model Complexes Using Multifrequency (17)O-Hyperfine EPR Spectroscopies and Density Functional Theory
- 2015
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 119:43, s. 13904-13921
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Tidskriftsartikel (refereegranskat)abstract
- Multifrequency pulsed EPR data are reported for a series of oxygen bridged (μ-oxo/μ-hydroxo) bimetallic manganese complexes where the oxygen is labeled with the magnetically active isotope (17)O (I = 5/2). Two synthetic complexes and two biological metallocofactors are examined: a planar bis-μ-oxo bridged complex and a bent, bis-μ-oxo-μ-carboxylato bridge complex; the dimanganese catalase, which catalyzes the dismutation of H2O2 to H2O and O2, and the recently identified manganese/iron cofactor of the R2lox protein, a homologue of the small subunit of the ribonuclotide reductase enzyme (class 1c). High field (W-band) hyperfine EPR spectroscopies are demonstrated to be ideal methods to characterize the (17)O magnetic interactions, allowing a magnetic fingerprint for the bridging oxygen ligand to be developed. It is shown that the μ-oxo bridge motif displays a small positive isotropic hyperfine coupling constant of about +5 to +7 MHz and an anisotropic/dipolar coupling of -9 MHz. In addition, protonation of the bridge is correlated with an increase of the hyperfine coupling constant. Broken symmetry density functional theory is evaluated as a predictive tool for estimating hyperfine coupling of bridging species. Experimental and theoretical results provide a framework for the characterization of the oxygen bridge in Mn metallocofactor systems, including the water oxidizing cofactor of photosystem II, allowing the substrate/solvent interface to be examined throughout its catalytic cycle.
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| 9. |
- Rapatskiy, Leonid, et al.
(författare)
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Detection of the Water-Binding Sites of the Oxygen-Evolving Complex of Photosystem II Using W-Band 17O Electron–Electron Double Resonance-Detected NMR Spectroscopy
- 2012
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Ingår i: Journal of the American Chemical Society. - Washington : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 134:40, s. 16619-16634
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Tidskriftsartikel (refereegranskat)abstract
- Water binding to the Mn4O5Ca cluster of the oxygen-evolving complex (OEC) of Photosystem II (PSII) poised in the S2 state was studied via H217O- and 2H2O-labeling and high-field electron paramagnetic resonance (EPR) spectroscopy. Hyperfine couplings of coordinating 17O (I = 5/2) nuclei were detected using W-band (94 GHz) electron–electron double resonance (ELDOR) detected NMR and Davies/Mims electron–nuclear double resonance (ENDOR) techniques. Universal 15N (I = 1/2) labeling was employed to clearly discriminate the 17O hyperfine couplings that overlap with 14N (I = 1) signals from the D1-His332 ligand of the OEC (Stich Biochemistry 2011, 50 (34), 7390−7404). Three classes of 17O nuclei were identified: (i) one μ-oxo bridge; (ii) a terminal Mn–OH/OH2 ligand; and (iii) Mn/Ca–H2O ligand(s). These assignments are based on 17O model complex data, on comparison to the recent 1.9 Å resolution PSII crystal structure (Umena Nature 2011, 473, 55−60), on NH3 perturbation of the 17O signal envelope and density functional theory calculations. The relative orientation of the putative 17O μ-oxo bridge hyperfine tensor to the 14N(15N) hyperfine tensor of the D1-His332 ligand suggests that the exchangeable μ-oxo bridge links the outer Mn to the Mn3O3Ca open-cuboidal unit (O4 and O5 in the Umena et al. structure). Comparison to literature data favors the Ca-linked O5 oxygen over the alternative assignment to O4. All 17O signals were seen even after very short (≤15 s) incubations in H217O suggesting that all exchange sites identified could represent bound substrate in the S1 state including the μ-oxo bridge. 1H/2H (I = 1/2, 1) ENDOR data performed at Q- (34 GHz) and W-bands complement the above findings. The relatively small 1H/2H couplings observed require that all the μ-oxo bridges of the Mn4O5Ca cluster are deprotonated in the S2 state. Together, these results further limit the possible substrate water-binding sites and modes within the OEC. This information restricts the number of possible reaction pathways for O–O bond formation, supporting an oxo/oxyl coupling mechanism in S4.
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| 10. |
- Satizabal, Claudia L., et al.
(författare)
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Genetic architecture of subcortical brain structures in 38,851 individuals
- 2019
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Ingår i: Nature Genetics. - : Nature Publishing Group. - 1061-4036 .- 1546-1718. ; 51:11, s. 1624-
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Tidskriftsartikel (refereegranskat)abstract
- Subcortical brain structures are integral to motion, consciousness, emotions and learning. We identified common genetic variation related to the volumes of the nucleus accumbens, amygdala, brainstem, caudate nucleus, globus pallidus, putamen and thalamus, using genome-wide association analyses in almost 40,000 individuals from CHARGE, ENIGMA and UK Biobank. We show that variability in subcortical volumes is heritable, and identify 48 significantly associated loci (40 novel at the time of analysis). Annotation of these loci by utilizing gene expression, methylation and neuropathological data identified 199 genes putatively implicated in neurodevelopment, synaptic signaling, axonal transport, apoptosis, inflammation/infection and susceptibility to neurological disorders. This set of genes is significantly enriched for Drosophila orthologs associated with neurodevelopmental phenotypes, suggesting evolutionarily conserved mechanisms. Our findings uncover novel biology and potential drug targets underlying brain development and disease.
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