Local water sensing: water exchange in bacterial photosynthetic reaction centers embedded in a trehalose glass studied using multiresonance EPR

Nalepa, Anna; Malferrari, Marco; Lubitz, Wolfgang; Venturoli, Giovanni; Möbius, K.; Savitsky, Anton

doi:10.1039/c7cp03942e

Cited by 19 publications

(15 citation statements)

References 89 publications

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“…FTIR studies in a wide range of water contents and temperatures, at fixed sugar/protein ratio, in different sugars [142,154,[165][166][167] hint at a tight protein-matrix dynamical coupling, attributed to the presence of the protein-medium HB network evidenced by MD results (or anchorage hypothesis, [137,138,154,[168][169][170]; see also Section 3.3). Besides the hydration, which tunes the switch from a locally structured solid to a honeyed liquid, the structure of a saccharide matrix is sizably determined by the relative amounts of sugar and embedded protein.…”

Section: Effect Of Saccharide Matrices On Protein Structure and Dynamicsmentioning

confidence: 96%

More than a Confinement: “Soft” and “Hard” Enzyme Entrapment Modulates Biological Catalyst Function

et al. 2019

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Catalysis makes chemical and biochemical reactions kinetically accessible. From a technological point of view, organic, inorganic, and biochemical catalysis is relevant for several applications, from industrial synthesis to biomedical, material, and food sciences. A heterogeneous catalyst, i.e., a catalyst confined in a different phase with respect to the reagents’ phase, requires either its physical confinement in an immobilization matrix or its physical adsorption on a surface. In this review, we will focus on the immobilization of biological catalysts, i.e., enzymes, by comparing hard and soft immobilization matrices and their effect on the modulation of the catalysts’ function. Indeed, unlike smaller molecules, the catalytic activity of protein catalysts depends on their structure, conformation, local environment, and dynamics, properties that can be strongly affected by the immobilization matrices, which, therefore, not only provide physical confinement, but also modulate catalysis.

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Section: Effect Of Saccharide Matrices On Protein Structure and Dynamicsmentioning

confidence: 96%

More than a Confinement: “Soft” and “Hard” Enzyme Entrapment Modulates Biological Catalyst Function

et al. 2019

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“…Details of our recent pulsed W-band (94 GHz) high-field multi-resonance EPR, ELDOR-detected NMR and ENDOR experiments on photosynthetic reaction center complexes, in conjunction with using nitroxide spin-labeled proteins as well as deuterium and 17 O isotope-labeled water [545][546][547], will be presented in Section 7, Case Study I.…”

Section: The Effect Of Protein-solvent Interactions For Biological Fumentioning

confidence: 99%

“…In our recent work, the bacterial reaction center (bRC) from Rhodobacter (Rb.) sphaeroides R26 embedded into a trehalose glass matrix was used as the model system [545]. The bRC hosts the two native radical cofactor ions P •+ 865 (primary electron donor) and Q •− A (primary electron acceptor) as well as an artificial nitroxide spin label site-specifically attached to the surface of the H-protein domain.…”

Section: Ednmr On Nitroxide Labeled Bacterial Reaction Centers Embeddmentioning

confidence: 99%

“…At this field range, the Larmor frequency, ν n , of many nuclei is significantly larger than 10 MHz, allowing for their detection by EDNMR. Over the last decade, a series of reports appeared that used high-field EDNMR to characterize a number of chemical systems and materials with a wide variety of nuclei in radical [228,236,545,[557][558][559][560][561][562][563][564] and transition metal containing systems [272,273,275,276,[565][566][567][568][569][570][571][572][573][574][575][576][577][578][579][580][581][582][583][584].…”

Section: Introductionmentioning

confidence: 99%

“…We also note that at high field, correlation transitions (those involving multiple nuclei) can be more easily suppressed that can contribute to the observed linewidth at lower microwave bands (X-, Q-band). In the text below we describe recent results from our laboratories on using EDNMR to characterize radicals and paramagnetic metal complexes at higher magnetic fields [236,273,274,545,558,559,[562][563][564]572,583]. For further information about the EDNMR method we refer the reader to recent reviews [274,585].…”

Section: Introductionmentioning

confidence: 99%

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Biomolecular EPR Meets NMR at High Magnetic Fields

et al. 2018

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In this review on advanced biomolecular EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR regarding the measurement of interactions and dynamics of large molecules embedded in fluid-solution or solid-state environments. Our focus is on the characterization of protein structure, dynamics and interactions, using sophisticated EPR spectroscopy methods. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultrafast electronics for signal data handling and processing have pushed the limits of EPR spectroscopy to new horizons reaching millimeter and sub-millimeter wavelengths and 15 T Zeeman fields. Expanding traditional applications to paramagnetic systems, spin-labeling of biomolecules has become a mainstream multifrequency approach in EPR spectroscopy. In the high-frequency/high-field EPR region, sub-micromolar concentrations of nitroxide spin-labeled molecules are now sufficient to characterize reaction intermediates of complex biomolecular processes. This offers promising analytical applications in biochemistry and molecular biology where sample material is often difficult to prepare in sufficient concentration for NMR characterization. For multifrequency EPR experiments on frozen solutions typical sample volumes are of the order of 250 μL (S-band), 150 μL (X-band), 10 μL (Q-band) and 1 μL (W-band). These are orders of magnitude smaller than the sample volumes required for modern liquid- or solid-state NMR spectroscopy. An important additional advantage of EPR over NMR is the ability to detect and characterize even short-lived paramagnetic reaction intermediates (down to a lifetime of a few ns). Electron–nuclear and electron–electron double-resonance techniques such as electron–nuclear double resonance (ENDOR), ELDOR-detected NMR, PELDOR (DEER) further improve the spectroscopic selectivity for the various magnetic interactions and their evolution in the frequency and time domains. PELDOR techniques applied to frozen-solution samples of doubly spin-labeled proteins allow for molecular distance measurements ranging up to about 100 Å. For disordered frozen-solution samples high-field EPR spectroscopy allows greatly improved orientational selection of the molecules within the laboratory axes reference system by means of the anisotropic electron Zeeman interaction. Single-crystal resolution is approached at the canonical g-tensor orientations—even for molecules with very small g-anisotropies. Unique structural, functional, and dynamic information about molecular systems is thus revealed that can hardly be obtained by other analytical techniques. On the other hand, the limitation to systems with unpaired electrons means that EPR is less widely used than NMR. However, this limitation also means that EPR offers greater specificity, since ordinary chemical solvents and matrices do not give rise to EPR in contrast to NMR spectra. Thus, multifrequency EPR spectroscopy plays an important role in better understanding paramagnetic species such as organic and inorganic radicals, transition metal complexes as found in many catalysts or metalloenzymes, transient species such as light-generated spin-correlated radical pairs and triplets occurring in protein complexes of photosynthetic reaction centers, electron-transfer relays, etc. Special attention is drawn to high-field EPR experiments on photosynthetic reaction centers embedded in specific sugar matrices that enable organisms to survive extreme dryness and heat stress by adopting an anhydrobiotic state. After a more general overview on methods and applications of advanced multifrequency EPR spectroscopy, a few representative examples are reviewed to some detail in two Case Studies: (I) High-field ELDOR-detected NMR (EDNMR) as a general method for electron–nuclear hyperfine spectroscopy of nitroxide radical and transition metal containing systems; (II) High-field ENDOR and EDNMR studies of the Oxygen Evolving Complex (OEC) in Photosystem II, which performs water oxidation in photosynthesis, i.e., the light-driven splitting of water into its elemental constituents, which is one of the most important chemical reactions on Earth.

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¹⁷O Hyperfine Spectroscopy Reveals Hydration Structure of Nitroxide Radicals in Aqueous Solutions

et al. 2022

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The hydration structure of nitroxide radicals in aqueous solutions is elucidated by advanced 17O hyperfine (hf) spectroscopy with support of quantum chemical calculations and MD simulations. A piperidine and a pyrrolidine‐based nitroxide radical are compared and show clear differences in the preferred directionality of H‐bond formation. We demonstrate that these scenarios are best represented in 17O hf spectra, where in‐plane coordination over σ ${\sigma }$ ‐type H‐bonding leads to little spin density transfer on the water oxygen and small hf couplings, whereas π ${{\rm \pi }}$ ‐type perpendicular coordination generates much larger hf couplings. Quantitative analysis of the spectra based on MD simulations and DFT predicted hf parameters is consistent with a distribution of close solvating water molecules, in which directionality is influenced by subtle steric effects of the ring and the methyl group substituents.

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Local water sensing: water exchange in bacterial photosynthetic reaction centers embedded in a trehalose glass studied using multiresonance EPR

Cited by 19 publications

References 89 publications

More than a Confinement: “Soft” and “Hard” Enzyme Entrapment Modulates Biological Catalyst Function

More than a Confinement: “Soft” and “Hard” Enzyme Entrapment Modulates Biological Catalyst Function

Biomolecular EPR Meets NMR at High Magnetic Fields

¹⁷O Hyperfine Spectroscopy Reveals Hydration Structure of Nitroxide Radicals in Aqueous Solutions

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Local water sensing: water exchange in bacterial photosynthetic reaction centers embedded in a trehalose glass studied using multiresonance EPR

Cited by 19 publications

References 89 publications

More than a Confinement: “Soft” and “Hard” Enzyme Entrapment Modulates Biological Catalyst Function

More than a Confinement: “Soft” and “Hard” Enzyme Entrapment Modulates Biological Catalyst Function

Biomolecular EPR Meets NMR at High Magnetic Fields

17O Hyperfine Spectroscopy Reveals Hydration Structure of Nitroxide Radicals in Aqueous Solutions

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¹⁷O Hyperfine Spectroscopy Reveals Hydration Structure of Nitroxide Radicals in Aqueous Solutions