Proteins relaxation phenomena

When a fluorophore is bound to a protein, its fluorescence will be dependent on the polarity of the surrounding amino acids. Fluorescence spectra are also dependent on the rigidity of the medium. The relaxation phenomenon (reorientation of the dipole environment) occurs much more easily in a fluid medium. In such a case, emission will occur after relaxation. This is the case when relaxation is faster than fluorescence, i.e., the relaxation lifetime rr is shorter than the fluorescence lifetime to- This occurs when the binding site is flexible, and the fluorophore can move easily. Emission from a relaxed state does not change with excitation wavelength. This can be explained by the fact that whatever the value of the excitation wavelength, the emission will always occur at the same energy level. 

These data demonstrate therefore that specific targets of the inhibitors of protein synthesis are involved in the relaxation phenomenon. ... 

The cross-correlation effects between the DD and CSA interactions also influence the transverse relaxation and lead to the phenomenon known as differential line broadening in a doublet [40], cf Figure Bl.13.8. There is a recent experiment, designed for protein studies, that I wish to mention at tire end of this section. It has been proposed by Pervushin etal [4T], is called TROSY (transverse relaxation optimized spectroscopy) and... 

The usefulness of NMR in such analysis is because the proton spin-relaxation time constants are different for different components, such as water, liquid fat and solid fat. For example, the signal from solid fat is found to decay rapidly while the liquid signals decay much slower. This phenomenon is the basis for an NMR technique to determine the solid fat content [20], However, as the relaxation time constant of water, for example, could depend on its local environment, such as protein concentration, it may overlap with that of oil and other components. As a result, it could be difficult to formulate a robust and universal relaxation analysis. It... 

To summarize, three conclusions transpire from the nanoscale thermodynamics results (a) The interfacial tension between protein and water is patchy and the result of both nanoscale confinement of interfacial water and local redshifts in dielectric relaxation (b) the poor hydration of polar groups (a curvature-dependent phenomenon) generates interfacial tension, a property previously attributed only to hydrophobic patches and (c) because of its higher occurrence at protein-water interfaces, the poorly hydrated dehydrons become collectively bigger contributors to the interfacial tension than the rarer nonpolar patches on the protein surface. 

Interest in water at protein surfaces and other surfaces arises from a desire to understand structural, functional, and dynamic factors as well as their interrelationships. Nuclear magnetic resonance (NMR) spectroscopy provides both structural and dynamic information. This presentation will focus on dynamical aspects of the water-protein Interaction. In particular, the phenomenon of cross relaxation between the water and protein proton systems will be discussed and new evidence will be reported. Failure to recognize the importance of cross relaxation effects leads to incorrect conclusions about the dynamics of water at protein surfaces. 

In this chapter, we describe mainly relaxation experiments to characterize protein backbone dynamics in solution. NMR spin-relaxation is a phenomenon in which perturbed magnetization is restored to statistical equilibrium by random fluctuations of local magnetic fields. The major local magnetic fields in diamagnetic proteins are generated by the amide dipolar interaction and chemical... 

Paramagnetic moieties exhibiting different relaxation times and spin quantum numbers modulate differently the longitudinal (Rj) and transverse (R2) relaxation rates of the protein H, and nuclei. Specifically, nitroxide, Cu° and Mn spin-labels cause considerable longitudinal nuclear PREs. The nitroxide and EDTA-Mn spin labels also generate large distance-dependent transverse relaxation enhancements, while this phenomenon is significantly attenuated for the Cu center. 

Small proteins and biopolymers of 1 pm sizes also possess the Debye-type orientation relaxation in MHz (for small molecules of several angstroms this relaxation would be in the GHz range) that can overlap with the P-relaxation. Small dipoles and molecules exhibiting rotational orientation, the relaxation mechanism can be approximated as spherical particles of radius a in solvent of viscosity i), where their charge z can often be assumed to be unity [6]. The high-frequency relaxation times corresponding to this phenomenon can be described in a simplified expression ... 

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