The dynamical transition in proteins of bacterial photosynthetic reaction centers observed by echo-detected EPR of specific spin labels

Wageningen University Laboratory of Biophysics Wageningen The Netherlands
Applied Magnetic Resonance (Impact Factor: 0.83). 01/2007; 31(1):159-166. DOI: 10.1007/BF03166253

ABSTRACT An echo-detected electron paramagnetic resonance (ED EPR) approach was used to study molecular dynamics in photosynthetic
reaction centers (RCs) fromRhodobacter sphaeroides R26, employing the specific spin label methanethiosulfonate and 3-maliemido proxyl. ED EPR has recently been shown to be
sensitive to so-called dynamical transition in disordered media, which is characterized by the transition from a harmonic-like
librational motion of a molecule to an anharmonic one or to a stochastic wobbling motion. ED EPR line shapes studied over
a wide temperature range reveal a sharp transition occurring above 180 K. The possible relation of the found transition to
the temperature dependence of electron transfer reactions in RC is discussed.

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    ABSTRACT: A new strategy has been applied that combines molecular dynamics (MD) simulations and electron paramagnetic resonance (EPR) spectroscopy to study the structure and conformational dynamics of the spin-labeled photosynthetic reaction center (RC) ofRhodobacter sphaeroides. This protein serves here as a model system to demonstrate the applicability of this new methodology. The RC contains five native cysteines and EPR experiments show that only one cysteine, located on the H subunit, is accessible for spin labeling. The EPR spectra calculated from MD simulation trajectories of spin labels bound to the native cysteines C156 and C234 in subunit H reveal that only the spin label side chain at position 156 provides a spectrum which agrees with the experimental EPR spectrum.
    Applied Magnetic Resonance 31(1):167-178. · 0.83 Impact Factor
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    ABSTRACT: When the dynamic properties of many different proteins are plotted as a function of temperature, biphasic behaviour is observed, with a broad transition centred around 220 K. Atomic mean-square displacements from X-ray crystallography and Mössbauer scattering show this behaviour, as do electron transfer rates and dynamic information from inelastic neutron scattering. Molecular dynamics simulations over a range of temperatures also exhibit a transition at about 220 K: high-temperature atomic fluctuations are dominated by anharmonic collective motions of bonded and nonbonded groups of atoms, but below 220 K the predominant dynamic behaviour is harmonic vibration of individual atoms. Here we show by high-resolution X-ray diffraction that crystalline ribonuclease A does not bind substrate or inhibitor at 212 K but will bind either rapidly at 228 K. Once bound at the higher temperature, inhibitor cannot be washed off after the enzyme is cooled to below the transition temperature. These results suggest that enzyme flexibility is required for catalytic function.
    Nature 07/1992; 357(6377):423-4. · 38.60 Impact Factor
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    ABSTRACT: Dynamics of tRNA was studied using neutron scattering spectroscopy. Despite vast differences in the architecture and backbone structure of proteins and RNA, hydrated tRNA undergoes the dynamic transition at the same temperature as hydrated lysozyme. The similarity of the dynamic transition in RNA and proteins supports the idea that it is solvent induced. Because tRNA essentially has no methyl groups, the results also suggest that methyl groups are not the main contributor of the dynamic transition in biological macromolecules. However, they may explain strong differences in the dynamics of tRNA and lysozyme observed at low temperatures.
    Journal of the American Chemical Society 02/2006; 128(1):32-3. · 10.68 Impact Factor

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