Electron paramagnetic resonance spectroscopy spin labels

Lagerstedt, J.O., Budamagunta, M.S., Oda, M.N., and Voss, J.C. 2007. Electron paramagnetic resonance spectroscopy of site-directed spin labels reveals the structural heterogeneity in the N-terminal domain of ApoA-I in solution. The Journal of Biological Chemistry 282 9143-9149. 

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... 

Studying RNA Using Site-Directed Spin-Labeling and Continuous-Wave Electron Paramagnetic Resonance Spectroscopy... 

Macosko, J. C., et al. (1999). A novel 5 displacement spin-labeling technique for electron paramagnetic resonance spectroscopy ofRNA. RNA 5, 1158-1166. 

Toolson, E.C., White, T. R. and Glaunsinger, W. S. (1979). Electron paramagnetic resonance spectroscopy of spin-labelled cuticle of Centruroides sculpturatus (Scorpiones Buthidae) correlation with thermal effects on cuticular permeability. 

The 2 -position has been used to attach other functional groups, either for detection or for further modification. The tertiary structure of TAR RNA has been investigated by the incorporation of the uridine analogue (35). " The analogue incorporates a nitroxide spin-label and may be detected using electron paramagnetic resonance spectroscopy (EPR). A similar spin-label has been attached to the of a guanosine residue, where it was used to monitor hybridisation by EPR. " ... 

Considerable international effort has since been directed towards these goals and substantial progress has been made in a number of directions. The development of accepted detection procedures not only gives enforcement authorities the ability to check that products are correctly labelled but also gives the consumer confidence that adequate independent controls are available. Perhaps the detection method that is, to date, the most internationally accepted is Electron Paramagnetic Resonance (EPR) spectroscopy which can also be referred to as Electron Spin Resonance (ESR) spectroscopy. 

Simatos et al. (1981) measured the mobility of a spin-label probe, TEMPO, a stable free radical commonly used for electron paramagnetic resonance (EPR) spectroscopy. She found that the probe showed no mobility below a critical that correlated to Wq. A critical a also existed at which the probe demonstrated a partitioning into a dissolved and a solid-like state. This critical a could represent the moisture content correlating to Tg, though this concept had not been introduced in foods at that time. The partitioning of a... 

Based on work at the Max Planck Institute for Polymer Research [172, 173], pulsed electron paramagnetic resonance (EPR) has experienced a remarkable revival worldwide [174]. In particular, pulsed double electron-electron resonance (DEER) spectroscopy in combination with site-directed spin labeling [175] is extensively used today in studies of the structure of proteins, including their function as carriers of small molecules, and of nucleic acids. Moreover, it is used to probe large, complex biomacromolecules and their assemblies as weU as 1361 protein folding [176]. 

Nitroxide radical spin labels can be used to measure inter-spin distances by pulsed electron paramagnetic resonance (EPR) spectroscopy, and to allow study of structure and folding of DNA and RNA ohgonucleotides [27-30]. Spin-labeling of nucleobases by (TuAAC in solution has first been demonstrated using the radical azide 4-azido-2,2,6,6-tetramethylpiperidine 1-oxyl (4-azido-TEMPO) [31], Alkyne modifications at position 7 of 7-deazapurines and C5-modified pyrimidines allowed attachment of the spin label in the major groove of duplex DNA [31]. In the same year, click chemistry on solid support to introduce spin labels into DNA was reported [32]. 

The technique of site-directed spin labeling (SDSL) provides information on bio-molecular systems by monitoring the behaviors of a stable radical tag (/.e spin label) using electron paramagnetic resonance (EPR) spectroscopy. SDSL studies of nucleic acids and protein-nucleic acid complexes have yielded unique information that is difficult to derive from other methods. In this chapter, we describe strategies used in nucleic acid SDSL investigations, and summarize advancements with a focus on those reported during the past five years. 

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