| 1. |
- Bhowmick, Asmit, et al.
(författare)
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Structural evidence for intermediates during O2 formation in photosystem II
- 2023
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Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 617:7961, s. 629-636
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Tidskriftsartikel (refereegranskat)abstract
- In natural photosynthesis, the light-driven splitting of water into electrons, protons and molecular oxygen forms the first step of the solar-to-chemical energy conversion process. The reaction takes place in photosystem II, where the Mn4CaO5 cluster first stores four oxidizing equivalents, the S0 to S4 intermediate states in the Kok cycle, sequentially generated by photochemical charge separations in the reaction center and then catalyzes the O–O bond formation chemistry. Here, we report room temperature snapshots by serial femtosecond X-ray crystallography to provide structural insights into the final reaction step of Kok’s photosynthetic water oxidation cycle, the S3→[S4]→S0 transition where O2 is formed and Kok’s water oxidation clock is reset. Our data reveal a complex sequence of events, which occur over micro- to milliseconds, comprising changes at the Mn4CaO5 cluster, its ligands and water pathways as well as controlled proton release through the hydrogen-bonding network of the Cl1 channel. Importantly, the extra O atom Ox, which was introduced as a bridging ligand between Ca and Mn1 during the S2→S3 transition, disappears or relocates in parallel with Yz reduction starting at approximately 700 μs after the third flash. The onset of O2 evolution, as indicated by the shortening of the Mn1–Mn4 distance, occurs at around 1,200 μs, signifying the presence of a reduced intermediate, possibly a bound peroxide.
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| 2. |
- Ohmer, Christopher J., et al.
(författare)
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XFEL serial crystallography reveals the room temperature structure of methyl-coenzyme M reductase
- 2022
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Ingår i: Journal of Inorganic Biochemistry. - : Elsevier BV. - 0162-0134 .- 1873-3344. ; 230, s. 111768-
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Tidskriftsartikel (refereegranskat)abstract
- Methyl-Coenzyme M Reductase (MCR) catalyzes the biosynthesis of methane in methanogenic archaea, using a catalytic Ni-centered Cofactor F430 in its active site. It also catalyzes the reverse reaction, that is, the anaerobic activation and oxidation, including the cleavage of the C-H bond in methane. Because methanogenesis is the major source of methane on earth, understanding the reaction mechanism of this enzyme can have massive implications in global energy balances. While recent publications have proposed a radical-based catalytic mechanism as well as novel sulfonate-based binding modes of MCR for its native substrates, the structure of the active state of MCR, as well as a complete characterization of the reaction, remain elusive. Previous attempts to structurally characterize the active MCR-Ni(I) state have been unsuccessful due to oxidation of the redox- sensitive catalytic Ni center. Further, while many cryo structures of the inactive Ni(II)-enzyme in various substrates bound forms have been published, no room temperature structures have been reported, and the structure and mechanism of MCR under physiologically relevant conditions is not known. In this study, we report the first room temperature structure of the MCRred1-silent Ni(II) form using an X-ray Free-Electron Laser (XFEL), with simultaneous X-ray Emission Spectroscopy (XES) and X-ray Diffraction (XRD) data collection. In celebration of the seminal contributions of inorganic chemist Dick Holm to our understanding of nickel-based catalysis, we are honored to announce our findings in this special issue dedicated to this remarkable pioneer of bioinorganic chemistry.
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| 3. |
- Kumar, Manish, et al.
(författare)
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Lead time of early warning by wastewater surveillance for COVID-19 : Geographical variations and impacting factors
- 2022
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 441
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Forskningsöversikt (refereegranskat)abstract
- The global data on the temporal tracking of the COVID-19 through wastewater surveillance needs to be comparatively evaluated to generate a proper and precise understanding of the robustness, advantages, and sensitivity of the wastewater-based epidemiological (WBE) approach. We reviewed the current state of knowledge based on several scientific articles pertaining to temporal variations in COVID-19 cases captured via viral RNA predictions in wastewater. This paper primarily focuses on analyzing the WBE-based temporal variation reported globally to check if the reported early warning lead-time generated through environmental surveillance is pragmatic or latent. We have compiled the geographical variations reported as lead time in various WBE reports to strike a precise correlation between COVID-19 cases and genome copies detected through wastewater surveillance, with respect to the sampling dates, separately for WASH and non-WASH countries. We highlighted sampling methods, climatic and weather conditions that significantly affected the concentration of viral SARS-CoV-2 RNA detected in wastewater, and thus the lead time reported from the various climatic zones with diverse WASH situations were different. Our major findings are: i) WBE reports around the world are not comparable, especially in terms of gene copies detected, lag-time gained between monitored RNA peak and outbreak/peak of reported case, as well as per capita RNA concentrations; ii) Varying sanitation facility and climatic conditions that impact virus degradation rate are two major interfering features limiting the comparability of WBE results, and iii) WBE is better applicable to WASH countries having well-connected sewerage system.
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