Rapid anisotropic motion of spin labels. models for motion averaging of the ESR parameters

Van, Shui Pong; Birrell, G. Bruce; Griffith, O. Hayes

doi:10.1016/0022-2364(74)90147-4

Cited by 68 publications

(57 citation statements)

References 8 publications

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“…However, the change in 2A zz with temperature can be used as an estimate of molecular motion (Van et al, 1974;Dzuba, 1996). A decrease in 2A zz is indicative of an increase in molecular mobility.…”

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confidence: 99%

Influence of Water Content and Temperature on Molecular Mobility and Intracellular Glasses in Seeds and Pollen

Buitink

Claessens

Hemminga³

et al. 1998

Plant Physiology

132

152

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Although the occurrence of intracellular glasses in seeds and pollen has been established, physical properties such as rotational correlation times and viscosity have not been studied extensively. Using electron paramagnetic resonance spectroscopy, we examined changes in the molecular mobility of the hydrophilic nitroxide spin probe 3-carboxy-proxyl during melting of intracellular glasses in axes of pea (Pisum sativum L.) seeds and cattail (Typha latifolia L.) pollen. The rotational correlation time of the spin probe in intracellular glasses of both organisms was approximately 10 ؊3 s. Using the distance between the outer extrema of the electron paramagnetic resonance spectrum (2A zz ) as a measure of molecular mobility, we found a sharp increase in mobility at a definite temperature during heating. This temperature increased with decreasing water content of the samples. Differential scanning calorimetry data on these samples indicated that this sharp increase corresponded to melting of the glassy matrix. Molecular mobility was found to be inversely correlated with storage stability. With decreasing water content, the molecular mobility reached a minimum, and increased again at very low water content. Minimum mobility and maximum storage stability occurred at a similar water content. This correlation suggests that storage stability might be at least partially controlled by molecular mobility. At low temperatures, when storage longevity cannot be determined on a realistic time scale, 2A zz measurements can provide an estimate of the optimum storage conditions.

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confidence: 99%

Influence of Water Content and Temperature on Molecular Mobility and Intracellular Glasses in Seeds and Pollen

Buitink

Claessens

Hemminga³

et al. 1998

Plant Physiology

132

152

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“…In electron paramagnetic resonance (EPR) spectroscopy, spectral simulations have been developed by a variety of approaches, including polar coordinates (2,3), spherical harmonics (4), and Eulerian transformations (5). Simulations can be fitted to experimental spectra employing MarquardtLevenberg least-squares routines (6) or the SIMPLEX algorithm (7).…”

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Determination of spin-label orientation within the myosin head.

Fajer

1994

Proc. Natl. Acad. Sci. U.S.A.

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Current methods of analyzing EPR spectra of spin-labeled muscle fibers allow the determination of spin-label orientation within the fiber, rather than the orientation of the myosin head itself. In order to describe the orientational distribution of spin labeled myosin heads within the muscle fibers, the orientation of the spin label within the myosin head must be known. The iodoacetamide label orientation in the myosin head was determined to be (16.8, 28.30, 4.2) or (16.6, 72.0, 4.30). These Eulerian angles were obtained from the analysis of EPR spectra of fibers decorated with labeled myosin heads in the absence of ATP, with the assumption that the head's tilt angle is 40°, as observed in a recent EM study [Pollard, T., Bbandari, D., Maupin, P., WachsstockD., Weeds, A. & Zot, H. (1993)Biophys. J. 64, 454-471]. Knowledge ofspin-label orientation will allow for qmntitative determination of myosin head orientation in the various states of the contractile cycle.Since the initial formulation ofthe rotating crossbridge theory (1), much effort has been expended on finding direct evidence for reorientation of the myosin head interacting with actin during muscle contraction. Rotation of the head is postulated to result in strain between the actin and myosin filaments, which is then relieved by the sliding ofthe filaments past each other. Structural studies have involved electron microscopy (EM), x-ray diffraction, and a variety of spectroscopic techniques sensitive to rotational motion. Each of these approaches has different limitations due to the complexity of data interpretation and artifacts due to sample preparation. Spectroscopy, magnetic or optical, has the major advantages of superior sensitivity to orientational changes and of site specificity-i.e., the ability to probe a single site on the protein. There is, however, a problem in translating spectroscopic signals into molecular terms. The problem can be broken into three separate topics: (i) development of simulation algorithms, (ii) optimization techniques to fit simulations to the observed spectra, and (iii) translating the orientational distributions of probes into the orientation of the molecules.In electron paramagnetic resonance (EPR) spectroscopy, spectral simulations have been developed by a variety of approaches, including polar coordinates (2, 3), spherical harmonics (4), and Eulerian transformations (5). Simulations can be fitted to experimental spectra employing MarquardtLevenberg least-squares routines (6) or the SIMPLEX algorithm (7). Alternatively, the orientational distribution of the spins can be determined by direct deconvolution of the spectral lineshape, rather than by fitting (8).Little attempt has been made in the area of relating the spin distribution to the molecular orientation. The stumbling block is the prerequisite of knowing the probe orientation within the molecule. Sometimes it is possible to determine the probe orientation from a single crystal of a protein by correlating the spin axis with the crystallographic axes (9, ...

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“…Simple models, based on partial averaging of nitroxide magnetic tensors, are applicable to the approximation of fast (subnanosecond) and restricted motion of a spin probe, and are useful to describe protein conformation at the labeling site (Timofeev and Nikolsky 2003; Van et al 1974). In this model, the EPR lineshape depends only on parameters describing the restriction of spin probe motion, e.g., the cone angle in a wobbling-in-cone model (Van et alprobe and protein, and potentials that reflect restrictions of these motions.…”

Section: Introductionmentioning

confidence: 99%

Protein Structural Dynamics Revealed by Site-Directed Spin Labeling and Multifrequency EPR

Nesmelov¹

2013

Protein Dynamics

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Multifrequency electron paramagnetic resonance (EPR), combined with site-directed spin labeling, is a powerful spectroscopic tool to characterize protein dynamics. The lineshape of an EPR spectrum reflects combined rotational dynamics of the spin probe's local motion within a protein, reorientations of protein domains, and overall protein tumbling. All these motions can be restricted and anisotropic, and separation of these motions is important for thorough characterization of protein dynamics. Multifrequency EPR distinguishes between different motions of a spin-labeled protein, due to the frequency dependence of EPR resolution to fast and slow motion of a spin probe. This gives multifrequency EPR its unique capability to characterize protein dynamics in great detail. In this review, we analyze what makes multifrequency EPR sensitive to different rates of spin probe motion and discuss several examples of its usage to separate spin probe dynamics and overall protein dynamics, to characterize protein backbone dynamics, and to resolve protein conformational states.

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Rapid anisotropic motion of spin labels. models for motion averaging of the ESR parameters

Cited by 68 publications

References 8 publications

Influence of Water Content and Temperature on Molecular Mobility and Intracellular Glasses in Seeds and Pollen

Influence of Water Content and Temperature on Molecular Mobility and Intracellular Glasses in Seeds and Pollen

Determination of spin-label orientation within the myosin head.

Protein Structural Dynamics Revealed by Site-Directed Spin Labeling and Multifrequency EPR

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