Electron spin label proteins

Sezer D, Freed JH, Roux B (2009) Multifrequency electron spin resonance spectra of a spin-labeled protein calculated from molecular dynamics simulations. J Am Chem Soc 131... 

Distances between paramagnetic centers in the range 3-13 nm can be measured by pulse techniques that record modulations due to the magnetic coupling between them. The modulations are caused by the interaction between the magnetic moments of the unpaired electrons. This method has been used to obtain distances within spin-labelled proteins, where the spin labels are free radicals that have been attached to amino acids at two known positions, and to dimeric biomolecules, each monomer containing a free radical. 

Clearly, the potential to use spin labels as a means to reduce protein concentration for detection of protein-ligand interactions, given by the factor of 6582, is tremendous. The sixth-power dependence on electron-proton distance underlines the need to carefully design the residue type which is to be spin labeled. Residues that can be spin labeled include lysine, tyrosine, cysteine, histidine, and methionine [7, 14]. At least one residue of... 

Based on our current understanding of ribosomal protein synthesis, several strategies have been developed to incorporate amino acids other than the 20 standard proteinogenic amino acids into a peptide using the ribosomal machinery . This allows for the design of peptides with novel properties. On the one hand, such a system can be used to synthesize nonstandard peptides that are important pharmaceuticals. In nature, such peptides are produced by nonribosomal peptide synthetases, which operate in complex pathways. On the other hand, non-natural residues are a useful tool in biochemistry and biophysics to study proteins. For example, incorporation of non-natural residues by the ribosome allows for site-specific labeling of proteins with spin labels for electron paramagnetic resonance spectroscopy, with... 

Selected entries from Methods in Enzymology [vol, page(s)] Electron paramagnetic resonance [effect on line width, 246, 596-598 motional narrowing spin label spectra, 246, 595-598 slow motion spin label spectra, 246, 598-601] helix-forming peptides, 246, 602-605 proteins, 246, 595 Stokes-Einstein relationship, 246, 594-595 temperature dependence, 246, 602, 604. 

Fourier Deconvolution. A synthetic 30-residue polypeptide was synthesized as an electron-transfer protein.42 A spin label was attached at position 21 and the distance between the two labels in a dimer was determined by Fourier deconvolution of the CW line-shape in frozen solution. Based on the known geometry of the label, it was calculated that the interspin distance of 22.5 A corresponded to 13.5 + 0.9 A between the Ca carbons on the two polypeptide chains. 

EPR spectroscopy is used widely in the study of proteins and of lipid-protein interactions.0 It has often been used to estimate distances between spin labels and bound paramagnetic metal ions.g A high-resolution EPR technique that detects NMR transitions by a simultaneously irradiated EPR transition is known as electron-nuclear double resonance (ENDOR).h... 

Pali, T., Finbow, M. E., Holzenburg, A., Findlay, J. B., and Marsh, D. (1995). Lipid-protein interactions and assembly of the 16-kDa channel polypeptide from Nephrops norvegicus Studies with spin-label electron spin resonance spectroscopy and electron microscopy. Biochemistry 34, 9211-9218. 

Fajer, P. G. (2000). Electron spin resonance spectroscopy labeling in proteins and peptides analysis. In Encyclopedia of Analytical Chemistry, (R. Meyers, ed.), pp. 5725-5761. Wiley, Chichester. 

The traditional fluorescence and electron-spin resonance methods for recording molecular collisions do not allow the study of translational diffusion and rare encounters of molecules in a viscous media because of the short characteristic times of these methods. To measure the rate constants of rare encounters between macromolecules and to investigate the translation diffusion of labelled proteins and probes in a medium of high viscosity (like biomembranes), a new triplet-photochrome labeling technique has been developed (Mekler and Likhtenshtein, 1986 Mekler and Umarova, 1988 Likhtenshtein, 1993 Papper and Likhtenshtein, 2001). 

In solving problems of enzyme catalysis, molecular biophysics of proteins, biomembranes and molecular biology it is necessary to know the spatial disposition of individual parts. One must also know the depth of immersion of paramagnetic centers in a biological matrix, i.e. the availability of enzyme sites to substrates, distance of electron tunneling between a donor and an acceptor group, position of a spin-label in a membrane and in a protein globule, distribution of the electrostatic field around the PC, etc. 

The compensation phenomena considered above are not only characterise of enzyme reactions. The compensation relationships in protein denaturation are noted for enormous ranges of Ea values (from 0 to 120 kcal/mole) and AS of (from 10 to 400 eu) (Likhtenshtein and Troshkina, 1968). These quantities have been found to be highly sensitive to to external condidion (pH, additive, moisture content, etc.) and rotational diffusion of spin labels introduced into various portions of globular proteins. They have also been observed, though to a less extend, in various processes in the condenced phase (chemical reactions, diffusion, evaporation, electrical, conduction, electron transfer, etc. The main property of all these systems, which differ from simple gas reactions, is the cooperative behavior of particle assemblies surrounding the reaction centers. 

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