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Nilsson, Håkan
Publications (9 of 9) Show all publications
Chrysina, M., Heyno, E., Kutin, Y., Reus, M., Nilsson, H., Nowaczyk, M. M., . . . Cox, N. (2019). Five-coordinate Mn-IV intermediate in the activation of nature's water splitting cofactor. Proceedings of the National Academy of Sciences of the United States of America, 116(34), 16841-16846
Open this publication in new window or tab >>Five-coordinate Mn-IV intermediate in the activation of nature's water splitting cofactor
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2019 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 116, no 34, p. 16841-16846Article in journal (Refereed) Published
Abstract [en]

Nature's water splitting cofactor passes through a series of catalytic intermediates (S-0-S-4) before O-O bond formation and O-2 release. In the second last transition (S-2 to S-3) cofactor oxidation is coupled to water molecule binding to Mn1. It is this activated, water-enriched all Mn-IV form of the cofactor that goes on to form the O-O bond, after the next light-induced oxidation to S-4. How cofactor activation proceeds remains an open question. Here, we report a so far not described intermediate (S-3') in which cofactor oxidation has occurred without water insertion. This intermediate can be trapped in a significant fraction of centers (> 50%) in (i) chemical-modified cofactors in which Ca2+ is exchanged with Sr2+; the Mn4O5Sr cofactor remains active, but the S-2-S-3 and S-3-S-0 transitions are slower than for the Mn4O5Ca cofactor; and (ii) upon addition of 3% vol/vol methanol; methanol is thought to act as a substrate water analog. The S-3' electron paramagnetic resonance (EPR) signal is significantly broader than the untreated S-3 signal (2.5 T vs. 1.5 T), indicating the cofactor still contains a 5-coordinate Mn ion, as seen in the preceding S-2 state. Magnetic double resonance data extend these findings revealing the electronic connectivity of the S-3' cofactor is similar to the high spin form of the preceding S-2 state, which contains a cuboidal Mn3O4Ca unit tethered to an external, 5-coordinate Mn ion (Mn-4). These results demonstrate that cofactor oxidation regulates water molecule insertion via binding to Mn-4. The interaction of ammonia with the cofactor is also discussed.

Keywords
Photosystem II, WOC/OEC, EPR, EDNMR, methanol
National Category
Organic Chemistry
Identifiers
urn:nbn:se:umu:diva-163062 (URN)10.1073/pnas.1817526116 (DOI)000481935500034 ()31391299 (PubMedID)
Funder
Swedish Research Council, 2016-05183
Available from: 2019-10-17 Created: 2019-10-17 Last updated: 2019-10-17Bibliographically approved
Nilsson, H., Cournac, L., Rappaport, F., Messinger, J. & Lavergne, J. (2016). Estimation of the driving force for dioxygen formation in photosynthesis. Biochimica et Biophysica Acta - Bioenergetics, 1857(1), 23-33
Open this publication in new window or tab >>Estimation of the driving force for dioxygen formation in photosynthesis
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2016 (English)In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1857, no 1, p. 23-33Article in journal (Refereed) Published
Abstract [en]

Photosynthetic water oxidation to molecular oxygen is carried out by photosystem II (PSII) over a reaction cycle involving four photochemical steps that drive the oxygen-evolving complex through five redox states S-i (i = 0, ... , 4). For understanding the catalytic strategy of biological water oxidation it is important to elucidate the energetic landscape of PSII and in particular that of the final S-4 --> S-0 transition. In this short-lived chemical step the four oxidizing equivalents accumulated in the preceding photochemical events are used up to form molecular oxygen, two protons are released and at least one substrate water molecule binds to the Mn4CaO5 cluster. In this study we probed the probability to form S-4 from S-0 and O-2 by incubating YD-less PSII in the S-0 state for 2-3 days in the presence of O-18(2) and (H2O)-O-16. The absence of any measurable O-16,18(2) formation by water-exchange in the S-4 state suggests that the S-4 state is hardly ever populated. On the basis of a detailed analysis we determined that the equilibrium constant K of the S-4 --> S-0 transition is larger than 1.0 x 10(7) so that this step is highly exergonic. We argue that this finding is consistent with current knowledge of the energetics of the S-0 to S-4 reactions, and that the high exergonicity is required for the kinetic efficiency of PSII.

Keywords
Photosystem II, Water-oxidizing complex (WOC), Oxygen-evolving complex (OEC), Equilibrium nstant for S-4 -> S-0 transition
National Category
Bioenergy
Identifiers
urn:nbn:se:umu:diva-114010 (URN)10.1016/j.bbabio.2015.09.011 (DOI)000366771700004 ()2-s2.0-84945292104 (Scopus ID)
Available from: 2016-01-25 Created: 2016-01-11 Last updated: 2018-06-07Bibliographically approved
Young, I. D., Ibrahim, M., Chatterjee, R., Gul, S., Fuller, F. D., Koroidov, S., . . . Yano, J. (2016). Structure of photosystem II and substrate binding at room temperature. Nature, 540(7633), 453-457
Open this publication in new window or tab >>Structure of photosystem II and substrate binding at room temperature
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2016 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 540, no 7633, p. 453-457Article in journal (Refereed) Published
Abstract [en]

Light-induced oxidation of water by photosystem II (PS II) in plants, algae and cyanobacteria has generated most of the dioxygen in the atmosphere. PS II, a membrane-bound multi-subunit pigment protein complex, couples the one-electron photochemistry at the reaction centre with the four-electron redox chemistry of water oxidation at the Mn4CaO5 cluster in the oxygen-evolving complex (OEC). Under illumination, the OEC cycles through five intermediate S-states (S0 to S4)1, in which S1 is the dark-stable state and S3 is the last semi-stable state before O–O bond formation and O2 evolution2,3. A detailed understanding of the O–O bond formation mechanism remains a challenge, and will require elucidation of both the structures of the OEC in the different S-states and the binding of the two substrate waters to the catalytic site4–6. Here we report the use of femtosecond pulses from an X-ray free electron laser (XFEL) to obtain damage-free, room temperature structures of dark-adapted (S1), two-flash illuminated (2F; S3-enriched), and ammonia-bound two-flash illuminated (2F-NH3; S3-enriched) PS II. Although the recent 1.95 Å resolution structure of PS II at cryogenic temperature using an XFEL7 provided a damage-free view of the S1 state, measurements at room temperature are required to study the structural landscape of proteins under functional conditions8,9, and also for in situ advancement of the S-states. To investigate the water-binding site(s), ammonia, a water analogue, has been used as a marker, as it binds to the Mn4CaO5 cluster in the S2 and S3 states10. Since the ammonia-bound OEC is active, the ammonia-binding Mn site is not a substrate water site10–13. This approach, together with a comparison of the native dark and 2F states, is used to discriminate between proposed O–O bond formation mechanisms.

Place, publisher, year, edition, pages
Macmillan Publishers Ltd., 2016
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-128748 (URN)10.1038/nature20161 (DOI)000389716800046 ()27871088 (PubMedID)
Available from: 2016-12-14 Created: 2016-12-14 Last updated: 2018-06-09Bibliographically approved
Nilsson, H. (2014). Substrate water binding to the oxygen-evolving complex in photosystem II. (Doctoral dissertation). Umeå: Umeå Universitet
Open this publication in new window or tab >>Substrate water binding to the oxygen-evolving complex in photosystem II
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Oxygenic photosynthesis in plants, algae and cyanobacteria converts sunlight into chemical energy. In this process electrons are transferred from water molecules to CO2 leading to the assembly of carbohydrates, the building blocks of life. A cluster of four manganese ions and one calcium ion, linked together by five oxygen bridges, constitutes the catalyst for water oxidation in photosystem II (Mn4CaO5 cluster). This cluster stores up to four oxidizing equivalents (S0,..,S4 states), which are then used in a concerted reaction to convert two substrate water molecules into molecular oxygen. The reaction mechanism of this four-electron four-proton reaction is not settled yet and several hypotheses have been put forward. The work presented in this thesis aims at clarifying several aspects of the water oxidation reaction by analyzing the mode of substrate water binding to the Mn4CaO5 cluster.

Time-resolved membrane-inlet mass spectrometric detection of flash-induced O2 production after fast H218O labelling was employed to study the exchange rates between substrate waters bound to the Mn4CaO5 cluster and the surrounding bulk water. By employing this approach to dimeric photosystem II core complexes of the red alga Cyanidoschyzon merolae it was demonstrated that both substrate water molecules are already bound in the S2 state of the Mn4CaO5 cluster. This was confirmed with samples from the thermophilic cyanobacterium Thermosynechococcus elongatus. Addition of the water analogue ammonia, that is shown to bind to the Mn4CaO5 cluster by replacing the crystallographic water W1, did not significantly affect the exchange rates of the two substrate waters. Thus, these experiments exclude that W1 is a substrate water molecule.

The mechanism of O-O bond formation was studied by characterizing the substrate exchange in the S3YZ● state. For this the half-life time of this transient state into S0 was extended from 1.1 ms to 45 ms by replacing the native cofactors Ca2+ and Cl- by Sr2+ and I-. The data show that both substrate waters exchange significantly slower in the S3YZ● state than in the S3 state. A detailed discussion of this finding lead to the conclusions that (i) the calcium ion in the Mn4CaO5 cluster is not a substrate binding site and (ii) O-O bond formation occurs via the direct coupling between two Mn-bound water-derived oxygens, which were assigned to be the terminal water/hydroxy ligand W2 and the central oxo-bridging O5.

The driving force for the O2 producing S4→S0 transition was studied by comparing the effects of N2 and O2 pressures of about 20 bar on the flash-induced O2 production of photosystem II samples containing either the native cofactors Ca2+ and Cl- or the surrogates Sr2+ and Br-. While for the Ca/Cl-PSII samples no product inhibition was observed, a kinetic limitation of O2 production was found for the Sr/Br-PSII samples under O2 pressure. This was tentatively assigned to a significant slowdown of the O2 release in the Sr/Br-PSII samples. In addition, the equilibrium between the S0 state and the early intermediates of the S4 state family was studied under 18O2 atmosphere in photosystem II centers devoid of tyrosine YD. Water-exchange in the transiently formed early S4 states would have led to 16,18O2 release, but none was observed during a three day incubation time. Both experiments thus indicate that the S4→S0 transition has a large driving force. Thus, photosynthesis is not limited by the O2 partial pressure in the atmosphere.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2014. p. 51
Keywords
Photosynthesis, Photosystem II, water oxidation, oxygen evolution, substrate water exchange, membrane-inlet mass spectrometry
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-86500 (URN)978-91-7459-802-5 (ISBN)
Public defence
2014-03-20, KBC huset, Stora Hörsalen, KB3B1, Umeå universitet, Linnaeus väg 10, SE-901 87 Umeå, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2014-03-06 Created: 2014-02-27 Last updated: 2018-06-08Bibliographically approved
Nilsson, H., Krupnik, T., Kargul, J. & Messinger, J. (2014). Substrate water exchange in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae. Biochimica et Biophysica Acta - Bioenergetics, 1837(8), 1257-1262
Open this publication in new window or tab >>Substrate water exchange in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae
2014 (English)In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1837, no 8, p. 1257-1262Article in journal (Other academic) Published
Abstract [en]

The binding affinity of the two substrate–water molecules to the water-oxidizing Mn4CaO5 catalyst in photosystem II core complexes of the extremophilic red alga Cyanidioschyzon merolae was studied in the S2and S3 states by the exchange of bound 16O-substrate against 18O-labeled water. The rate of this exchange was detected via the membrane-inlet mass spectrometric analysis of flash-induced oxygen evolution. For both redox states a fast and slow phase of water-exchange was resolved at the mixed labeled m/z 34 mass peak: kf = 52 ± 8 s− 1 and ks = 1.9 ± 0.3 s− 1 in the S2 state, and kf = 42 ± 2 s− 1 and kslow = 1.2 ± 0.3 s− 1 in S3, respectively. Overall these exchange rates are similar to those observed previously with preparations of other organisms. The most remarkable finding is a significantly slower exchange at the fast substrate–water site in the S2 state, which confirms beyond doubt that both substrate–water molecules are already bound in the S2 state. This leads to a very small change of the affinity for both the fast and the slowly exchanging substrates during the S2 → S3 transition. Implications for recent models for water-oxidation are briefly discussed.

Keywords
Cyanidioschyzon merolae, photosystem II, Water oxidation, oxygen evolution, substrate–water exchange, membrane-inlet mass spectrometry
National Category
Chemical Engineering Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-86497 (URN)10.1016/j.bbabio.2014.04.001 (DOI)000339133800004 ()
Note

This paper is dedicated to the memory of Warwick Hillier (18.10.1967-10.01.2014). Using membrane-inlet mass spectrometry and FTIR spectroscopy Warwick made many important discoveries regarding substrate-water binding to the OEC and the mechanism of water-oxidation. He was a very good scientist and friend that was highly appreciated throughout the photosynthesis community. In 2007 he was awarded the Robin-Hill award of the International Society for Photosynthesis Research (ISPR).

Available from: 2014-02-27 Created: 2014-02-27 Last updated: 2018-06-08Bibliographically approved
Nilsson, H., Rappaport, F., Boussac, A. G. & Messinger, J. (2014). Substrate-water exchange in photosystem II is arrested before dioxygen formation. Nature Communications, 5, 4305
Open this publication in new window or tab >>Substrate-water exchange in photosystem II is arrested before dioxygen formation
2014 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 5, p. 4305-Article in journal (Refereed) Published
Abstract [en]

Light-driven oxidation of water into dioxygen, catalysed by the oxygen-evolving complex (OEC) in photosystem II, is essential for life on Earth and provides the blueprint for devices for producing fuel from sunlight. Although the structure of the OEC is known at atomic level for its dark-stable state, the mechanism by which water is oxidized remains unsettled. Important mechanistic information was gained in the past two decades by mass spectrometric studies of the H2 18O/H2 16O substrate-water exchange in the four (semi) stable redox states of the OEC. However, until now such data were not attainable in the transient states formed immediately before the O-O bond formation. Using modified photosystem II complexes displaying up to 40-fold slower O2 production rates, we show here that in the transient state the substrate-water exchange is dramatically slowed as compared with the earlier S states. This further constrains the possible sites for substrate-water binding in photosystem II.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-91401 (URN)10.1038/ncomms5305 (DOI)000340613800013 ()
Available from: 2014-08-04 Created: 2014-08-04 Last updated: 2018-06-07Bibliographically approved
Navarro, M. P., Ames, W. M., Nilsson, H., Lohmiller, T., Pantazis, D. A., Rapatskiy, L., . . . Cox, N. (2013). Ammonia binding to the oxygen-evolving complex of photosystem II identifies the solvent-exchangeable oxygen bridge (µ-oxo) of the manganese tetramer. Proceedings of the National Academy of Sciences of the United States of America, 110(39), 15561-15566
Open this publication in new window or tab >>Ammonia binding to the oxygen-evolving complex of photosystem II identifies the solvent-exchangeable oxygen bridge (µ-oxo) of the manganese tetramer
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2013 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 110, no 39, p. 15561-15566Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
PSII, OEC, water oxidizing complex, water-oxidation, Mn cluster
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-82288 (URN)10.1073/pnas.1304334110 (DOI)000324765100024 ()
Available from: 2014-02-18 Created: 2013-10-29 Last updated: 2018-06-08Bibliographically approved
Björnham, O., Nilsson, H., Andersson, M. & Schedin, S. (2009). Physical properties of the specific PapG–galabiose binding in E. coli P pili-mediated adhesion. European Biophysics Journal, 38(2), 245-254
Open this publication in new window or tab >>Physical properties of the specific PapG–galabiose binding in E. coli P pili-mediated adhesion
2009 (English)In: European Biophysics Journal, ISSN 0175-7571, E-ISSN 1432-1017, Vol. 38, no 2, p. 245-254Article in journal (Refereed) Published
Abstract [en]

Detailed analyses of the mechanisms thatmediate binding of the uropathogenic Escherichia coli tohost cells are essential, as attachment is a prerequisite forthe subsequent infection process. We explore, by means offorce measuring optical tweezers, the interaction betweenthe galabiose receptor and the adhesin PapG expressed byP pili on single bacterial cells. Two variants of dynamicforce spectroscopy were applied based on constant andnon-linear loading force. The specific PapG–galabiosebinding showed typical slip-bond behaviour in the forceinterval (30–100 pN) set by the pilus intrinsic biomechanicalproperties. Moreover, it was found that the bondhas a thermodynamic off-rate and a bond length of2.6×10-3 s-1 and 5.0 Å , respectively. Consequently, thePapG–galabiose complex is significantly stronger thanthe internal bonds in the P pilus structure that stabilizes thehelical chain-like macromolecule. This finding suggeststhat the specific binding is strong enough to enable the Ppili rod to unfold when subjected to strong shear forces inthe urinary tract. The unfolding process of the P pili rodpromotes the formation of strong multipili interaction,which is important for the bacterium to maintain attachmentto the host cells.

Place, publisher, year, edition, pages
New York: Springer, 2009
Keywords
Escherichia coli, Non-covalent single bond, Slip-bond, Dynamic force spectroscopy, Receptor–ligand interaction
National Category
Cell Biology Biochemistry and Molecular Biology
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-19734 (URN)10.1007/s00249-008-0376-y (DOI)000262671600011 ()
Available from: 2009-03-10 Created: 2009-03-10 Last updated: 2018-06-09Bibliographically approved
Nilsson, H., Han, G., Shevela, D., Cournac, L., Boussac, A., Rappaport, F., . . . Lavergne, J. Estimation of the equilibrium constant of the molecular oxygen generating S4→S0 (S3+YZ•→S0YZ) transition in photosystem II.
Open this publication in new window or tab >>Estimation of the equilibrium constant of the molecular oxygen generating S4→S0 (S3+YZ→S0YZ) transition in photosystem II
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(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-86499 (URN)
Available from: 2014-02-27 Created: 2014-02-27 Last updated: 2018-06-08
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