Proteins paramagnetic

Combines sensitivity of EPR and high resolution of NMR to probe ligand superhyperfine interactions For paramagnetic proteins enhanced chemical shift resolution, contact and dipolar shifts, spin delocalization, magnetic coupling from temperature dependence of shifts Identification of ligands coordinated to a metal centre... 

This chapter considers the distribution of spin Hamiltonian parameters and their relation to conformational distribution of biomolecular structure. Distribution of a g-value or g-strain leads to an inhomogeneous broadening of the resonance line. Just like the g-value, also the linewidth, W, in general, turns out to be anisotropic, and this has important consequences for powder patterns, that is, for the shape of EPR spectra from randomly oriented molecules. A statistical theory of g-strain is developed, and it is subsequently found that a special case of this theory (the case of full correlation between strain parameters) turns out to properly describe broadening in bioEPR. The possible cause and nature of strain in paramagnetic proteins is discussed. 

The situation found in Figure 13.6 (i.e., a cell with thousands of proteins but only one or two EPR signals) is also exemplary for what one typically finds when a recombinant paramagnetic protein is overexpressed in a standard host like E. coli. The overexpressed protein will give an EPR signal, and the background of the host is hardly detectable. The literature contains numerous examples from which we randomly cite a few (Uhlmann et al. 1997 Gaudu et al. 1997 Gao-Sheridan et al. 1998). 

Han S, Czernuszewicz RS, Kimura T, et al. 1989a. Fe2S2 protein resonance Raman revisited structural variations among adrenodoxin, ferredoxin, and red paramagnetic protein. J Am Chem Soc 111 3505-11. 

The magnetic susceptibility relaxation is usually more important for than for Ti. In fact, this mechanism is often dominant in determining the proton linewidth in paramagnetic proteins at high magnetic fields (3). Gillis and co-workers have recently developed a theory for the related case of proton linewidth in colloidal solutions of so-called superparamagnetic particles (54,55). 

Fig. 7. Mossbauer spectra of oxidized plant-type iron-sulfur proteins in zero applied magnetic field. Abbreviations AZI = A zotobacter Fe-S protein I, 4.6°K AZII = Azoiobacter Fe-S protein II, 4.2 °K Put. = Putidaredoxin, 4.2 °K Ad.— Pig Ad-renodoxin, 4.2 °K Clos. = Clostridial paramagnetic protein, 4.2 °K PPNR = Spinach ferredoxin, 4.5 °K Parsley = Parsley Ferredoxin, 4.2 °K. Velocity scale is relative to iron in platinum...

Fig. 8. Mossbauer spectra of oxidized plant-type iron-sulfur proteins in high applied magnetic field. Abbreviations Ad. = Pig Adrenodoxin, 4.2 °K, 46 kG PPNR = Spinach Ferredoxin, 4.5 °K, 50 kG Clos. = Clostridial Paramagnetic Protein, 4.2 °K, 46 kG AZI = Azotobacter Fe-S Protein I, 4.6°K, 46 kG AZII = Azotobacter Fe-S Protein II, 4.2 °K, 46 kG. Applied magnetic field is parallel to gamma-ray direction...

For a paramagnetic protein molecule such as deoxy-Hb, the 7V1 and 7V1 values in the absence of chemical exchange have been calculated as the sum of the dipole-dipole interactions... 

In this section, recent NMR studies of large paramagnetic proteins will be presented. The determination of the solution structures of small paramagnetic proteins will not be discussed, as this has been well covered in recent reviews.189190 The use of paramagnetic spin labels to introduce selective broadening of resonances and to probe solvent-exposed regions of proteins will also be discussed. 

Arnesano, R, Banci, L., Piccioli, M. (2005). NMR structures of paramagnetic proteins. Quarterly Reviews of Biophysics, 38, 167—219. 

Rast et al. studied the mechanisms of the intermolecular NMR relaxation dispersion of the tetramethylammonium protons in Gd " heavy-water solutions. The standard dipolar nuclear relaxation formalism of Solomon-Bloembergen, valid for the used frequency range between 10 and 800 MHz, leads to overall good agreement with the measured data without any adjustable parameters. Madhu et al. reported experimental observation and numerical simulation of a two-dimensional multiplet effect in the heteronuclear correlation spectrum of a paramagnetic protein that depends on molecular geometry. Bertini et performed solution structure calculations through self-... 

Cardenas, J., Mortenson, L.E., Yoch, D.C. Purification and Properties of Paramagnetic Protein from Clostridium pasteurianum W5, Biochim. Biophys. Acta 434, 244 (1976)... 

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