Spin labels of proteins

Hubbell, W.L., Gross, A., Langen, R., and Lietzow, M.A. 1998. Recent advances in site-directed spin labeling of proteins. Current Opinion in Structural Biology 8 649-656. 

Polyhach Y, Jeschke G (2010) Prediction of favourable sites for spin labelling of proteins. Spectroscopy 24 651-659... 

Kosen PA (1989) Spin labeling of proteins. Meth Enzymol 177 86—121... 

Finally, spin labeling of proteins, ESR oximetry, and the use of spin probes for investigation of the structure of biomembranes are classic examples of biological ESR. These topics have been discussed elsewhere in this encyclopedia. 

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... 

A highly reactive compound containing a neutral divalent carbon with two nonbondmg electrons (ie.,. CR2 or a substitution derivative). The nonbonding electrons can have parallel spins (triplet state) or antiparallel spins (singlet state). The parent species, iCRz, is also known as methylene. A number of carbene derivatives have been used as photoaffinity labels of proteins. Irradiation of 3 -0-(4-benzoyl)benzoyl-ATP will cause 70% inactivation of mitochondrial Fi-ATPase. ... 

Altenbach, C., et al. (1989). Structural studies on transmembrane proteins. 2. Spin labeling of bacteriorhodopsin mutants at unique cysteines. Biochemistry 28, 7806—7812. 

Feix, J.B. and Klug, C.S. (1998) Site-directed spin labeling of membrane proteins and peptide-membrane interaction, in Berliner, L. (eds.) Biological Magnetic Resonance 14, Spin Labeling the Next Millennium, Plenum Press, N.Y., pp. 250-315. 

Altenbach, C., Marti, T., Khorana, H. G., and Hubbell, W. L. (1990). Transmembrane protein structure spin labeling of bacteriorhodopsin mutants. Science 248, 1088-1092. 

C. Altenbach, T. Marti, H.G. Khorana, and W.L. Hubbell. 1990. Transmembrane protein structure Spin labeling of bacterio-rhodopsin mutants Science 248 1088-1092. (PubMed)... 

In modern experiments one is now able to place selectively spin labels in most any region of a biomolecule. This ability is stimulating an ever increasing usage of spin label EPR spectroscopy. In addition labeling of proteins and peptides, experiments have demonstrated that DNA may be labeled without perturbation of the double-helical structure. Analysis of DNA flexibility may provide important information toward the understanding of protein-DNA and drug-DNA interactions. 

Nitroxides can be used either as spin probes or as spin labels. Spin probes are subject to non-covalent interactions with the system under study. In many cases, spin probes very similar to one component of the system, e.g., spin-labeled lipids, are introduced. In contrast, spin labels are covalently linked to a complex structure, in many cases to a specific site, e.g., of a protein (SDSL) [10]. An alternative approach includes spin labeling of ligands interacting with the protein under study [11, 12]. 

Steinhoff HJ (1990) Residual motion of hemoglobin-bound spin labels and protein dynamics - viscosity dependence of the rotational correlation times. Eur Biophys J 18 57-62... 

Zou P, Mchaourab HS (2010) Increased sensitivity and extended range of distance measurements in spin-labeled membrane proteins Q-band double electron-electron resonance and nanoscale bilayers. Biophys J 98(6) L18-L20. doi DOI 10.1016/j. bpj.2009.12.4193... 

Bordignon E (2011) Site-directed spin labeling of membrane proteins. Top Curr Chem. doi 10.1007/128 2011 243... 

Site-Directed Spin Labeling of Membrane Proteins... 

Abstract EPR spectroscopy of site-directed spin labeled membrane proteins is at present a common and valuable biophysical tool to study structural details and conformational transitions under conditions relevant to function. EPR is considered a complementary approach to X-ray crystallography and NMR because it provides detailed information on (1) side chain dynamics with an exquisite sensitivity for flexible regions, (2) polarity and water accessibility profiles across the membrane bilayer, and (3) distances between two spin labeled side chains during protein functioning. Despite the drawback of requiring site-directed mutagenesis for each new piece of information to be collected, EPR can be applied to any complex membrane protein system, independently of its size. This chapter describes the state of the art in the application of site-directed spin labeling (SDSL) EPR to membrane proteins, with specific focus on the different types of information which can be obtained with continuous wave and pulsed techniques. 

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