Spin-labeled proteins

If site-specific spin-labeled protein is available [20], quantification of quenching effects on both first-site and second-site ligands can additionally aid in constructing a model of the ternary complex. 

Kulikov, A.V. (1976) Determination of distance between the nitroxide label and paramagnetic center in spin-labeled proteins from the parameters of the saturation curve of the ESR spectrum of the label at 77K. Molecul. Biol. (Moscow) 10, 109-116. 

Altenbach C, Cai K, Klein-Seetharaman J, Khorana HG, Hubbell WL. Estimation of inter-residue distances in spin labeled proteins at physiological temperatures experimental strategies and practical limitations. Biochemistry 2001 40 15471-15482. 

Figure 4 shows experimental data for maleimide-labeled hemoglobin in glycerol. A typical value of Tj for a spin-labeled protein is 10 s. 

Karim CB, Zhang Z, Thomas DD (2007) Synthesis of TOAC spin-labeled proteins and reconstitution in lipid membranes. Nat Protoc 2 42-49... 

Key steps to pave the way for the application to spin labeled proteins were performed by the group of Han [41]. 

Fig. 8 EPR detection of membrane insertion of spin labeled proteins, (a) NMR models of inactive Bax and Bid (PDB IF 16, 2BID, respectively). The buried helical hairpin is shown in orange, and the BH3 domain in yellow. Positions spin labeled in Bax are highlighted, (b) Kinetics of Bax conformational changes at 37 °C. Spectra of double labeled Bax were recorded each 43 s at 37 °C...

Oganesyan VS (2011) A general approach for prediction of motional EPR spectra from molecular dynamics (MD) simulations application to spin labelled protein. Phys Chem Chem Phys 13 4724 737... 

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... 

McCoy J, Hubbell WL (2011) High-pressure EPR reveals conformational equilibria and volumetric properties of spin-labeled proteins. Proc Natl Acad Sci USA 108(4) 1331-1336... 

Guo Z, Cascio D, Hideg K, Kalai T, Hubbell WL (2007) Structural determinants of nitroxide motion in spin-labeled proteins tertiary contact and solvent-inaccessible sites in helix G of T4 lysozyme. Prot Sci 16 1069-1086... 

Distances between paramagnetic centers in the range 2-8 nm can be measured by specialized pulse techniques that record modulations due to the magnetic coupling between them. The coupling is of the same type as for the fine-structure in radical pairs. By measuring the fine-structure constant D the distance is obtained. 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. 

Nadaud PS, Helmus JJ, Hofer N, Jaroniec CP (2007) Long-range structural restraints in spin-labeled proteins probed by solid-state nuclear magnetic resonance spectroscopy. J Am Chem... 

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