Spin Exchange

Molin, Yuri N.; Salikhov, K. M.; Zamaraev, K. I.

doi:10.1007/978-3-642-67666-6

Cited by 231 publications

(162 citation statements)

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“…Translational diffusion of oxygen in a membrane is presumably described by an axially symmetric tensor with the principal axis coinciding with the normal to the bilayer and with the magnitudes ofthe elements ofthe tensor dependent on the distance from the surface. The exchange integral is thought to be greater for an approach of oxygen to the spin label that occurs along the p. orbital than for approaches along x or y (23). In addition, y collisions are less effective because the nitroxide radical is protected by methyl groups on which the spin density is very low.…”

Section: Resultsmentioning

confidence: 99%

Oxygen transport parameter in membranes as deduced by saturation recovery measurements of spin-lattice relaxation times of spin labels.

Kusumi¹,

Subczynski²,

Hyde³

1982

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

153

180

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Spin-lattice relaxation time (T1) measurements of nitroxide radical spin labels in membranes have been made by using the saturation-recovery technique. Stearic acid and sterol-type labels were used as probes of dimyristoylphosphatidylcholine liposomes from 0 degrees C to 36 degrees C. In the absence of oxygen, the range of variation of T1 over all samples and conditions is about a factor of 3. Heisenberg exchange between oxygen and spin labels is an effective T1 mechanism for the spin labels. The full range of variation of T1 in the presence of air is about a factor of 100. It is suggested that the oxygen transport parameter W = T1(-1) (air) - T1(-1) (N2) is a useful new monitor of membrane fluidity that reports on translational diffusion of small molecules. The values of W change at the prephase and main phase transitions and vary in complex ways. Arguments are advanced that the data are indicative of anisotropic translational diffusion of oxygen.

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Section: Resultsmentioning

confidence: 99%

Oxygen transport parameter in membranes as deduced by saturation recovery measurements of spin-lattice relaxation times of spin labels.

Kusumi¹,

Subczynski²,

Hyde³

1982

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

153

180

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“…When the fibrils are formed by proteins spin-labeled at a specific site, the parallel in-register structure results in the stacking of spin labels in the fibrils. The stacked spin labels have strong spin exchange interactions, leading to the collapse of the three spectral lines to form a characteristic single-line EPR spectrum (24,39). Therefore, this single-line spectrum provides a convenient and powerful way to detect parallel in-register ␤ structure in the amyloid fibrils.…”

Section: Fibril Formation Of Ure2 Prion Domain-the Construct Ofmentioning

confidence: 99%

“…In these studies the EPR spectra of spin-labeled amyloid proteins show a single-line feature, whereas normally the EPR spectrum of a spin-labeled protein has three spectral lines. The single-line spectrum is a result of strong spin exchange interactions between stacked spin labels in the fibril (24,39). This single-line feature is a convenient and powerful signature to identify the parallel in-register ␤ structure in amyloids.…”

mentioning

confidence: 99%

Hierarchical Organization in the Amyloid Core of Yeast Prion Protein Ure2

Ngo

Guo

2011

Journal of Biological Chemistry

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Formation of amyloid fibrils is involved in a range of fatal human disorders including Alzheimer, Parkinson, and prion diseases. Yeast prions, despite differences in sequence from their mammalian counterparts, share similar features with mammalian prions including infectivity, prion strain phenomenon, and species barrier and thus are good model systems for human prion diseases. Yeast prions normally have long prion domains that presumably form multiple ␤ strands in the fibril, and structural knowledge about the yeast prion fibrils has been limited. Here we use site-directed spin labeling and electron paramagnetic resonance (EPR) spectroscopy to investigate the structures of amyloid fibrils of Ure2 prion domain. We show that 15 spin-labeled Ure2 mutants, with spin labels at every 5th residue from position 5 to position 75, show a single-line or nearly single-line feature in their EPR spectra as a result of strong spin exchange interactions. These results suggest that a parallel in-register ␤ structure exists at these spin-labeled positions. More interestingly, we also show that residues in the segment 30 -65 have stronger spin exchange interactions, higher local stability, and lower solvent accessibility than segments 5-25 and 70 -75, suggesting different local environment at these segments. We propose a hierarchical organization in the amyloid core of Ure2, with the segment 30 -65 forming an inner core and the segments 5-25 and 70 -75 forming an outer core. The hierarchical organization in the amyloid core may be a structural origin for polymorphism in fibrils and prion strains.

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“…Surprisingly, it contained only a single peak. Loss of the two outer peaks (hyperfine lines) is usually associated with spin exchange, and requires that, on the EPR time scale (Ͻ10 Ϫ7 s), multiple spin labels are in orbital overlap (20). Because of such temporal and spatial constraints, a single peak EPR spectrum is highly unusual for a spin-labeled protein.…”

Section: Spin Exchange Reveals Crystal-like Order In the Core Of Tau mentioning

confidence: 99%

“…Furthermore, spin interactions between labels provide distance constraints, which in addition with other structural information can be used for model building. Whereas dipolar interactions yield distance information in the range of 8 to 25 Å (19), a second type of interaction, spin exchange, is observed at smaller distances and requires orbital overlap (20).…”

mentioning

confidence: 99%

Template-assisted filament growth by parallel stacking of tau

Margittai

Langen

2004

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

250

264

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Tau Filaments are found in >20 neurodegenerative diseases. Yet, because of their enormous molecular weights and poor tendency to form highly ordered 3D crystal lattices, they have evaded high-resolution structure determination. Here, we studied 25 derivatized tau mutants by using electron paramagnetic resonance and fluorescence spectroscopy to report structural details of tau filaments. Based on strong spin exchange and pyrene excimer formation of core residues, we find that individual tau proteins form single molecule layers along the fiber axis that perfectly stack on top of each other by in-register, parallel alignment of ␤-strands. We suggest a model of filament growth wherein the existing filament serves as a template for the incoming, unfolded tau molecule, resulting in a new structured layer with maximized hydrogen-bonded contact surface and side-chain stacking. In addition to its role in stabilizing microtubules in neuritic extensions, tau has gained prominence as the protein constituent of filamentous inclusions in numerous neurodegenerative diseases (1). These inclusions, together with extracellular fibril deposits of the amyloid-␤ (A␤)-peptide, constitute the pathological hallmarks of Alzheimer's disease.In the adult human CNS, six different tau isoforms, ranging in size from 352 to 441 aa, are produced by alternative mRNA splicing. These isoforms vary by the absence or presence of the second of four microtubule-binding repeats in the C-terminal half and two inserts in the near N-terminal half of the protein (Fig. 1). The tau inclusions in Alzheimer's disease contain all six isoforms (2) and consist of paired helical and straight filaments (3, 4). Viewed under an electron microscope, tau filaments have a fuzzy coat that can be cleaved off by pronase (5). Cleavage leaves a core that is comprised of three microtubule-binding repeats (6). The importance of these repeats in filament formation was underscored by the finding that tau fragments comprising only the repeat region aggregate in vitro (7). In contrast, recombinant full-length tau is remarkably unreactive and aggregates only when anionic cofactors such as heparin are present (8,9).A recent study involving x-ray and selected area electron diffraction of both straight and paired helical filaments (10) revealed a common cross-␤ structure, with ␤-strands running perpendicular to the fiber axis. These data agreed with earlier findings of diffraction patterns from filaments obtained from shorter tau fragments (11,12). Importantly, they resolved some controversy concerning the filament structure of full-length tau (12)(13)(14). Thus, with respect to the cross-␤ structure and a seeded growth mechanism (15), tau filaments share similarities with a whole range of amyloidogenic protein aggregates (16). Beyond this, however, little is known about the structure of tau filaments. For example, it is not known how individual ␤-strands are arranged with each other and whether tau molecules align along or across the fiber axis, (i.e., whether hydrogen bonding among...

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Spin Exchange

Cited by 231 publications

References 0 publications

Oxygen transport parameter in membranes as deduced by saturation recovery measurements of spin-lattice relaxation times of spin labels.

Oxygen transport parameter in membranes as deduced by saturation recovery measurements of spin-lattice relaxation times of spin labels.

Hierarchical Organization in the Amyloid Core of Yeast Prion Protein Ure2

Template-assisted filament growth by parallel stacking of tau

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