Hydration and protein dynamics: an ESR and ST-ESR spin labelling study of human serum albumin

Abstract

Human serum albumin has been studied at low hydration level by the ESR spin labelling technique, under the assumption that a covalently bound spin-label is a reporter of the protein internal dynamics. At room temperature, the presence of a double component signal allowed us to monitor the influence of increasing hydration level on internal protein dynamics as well as on the superficial water dynamics. The ESR results have shown that the first 20 g of water per 100 g of protein activate the internal protein dynamics and that superficial water dynamics starts at higher hydration values. ESR expe¡ at low temperature have shown that at --l£176 ~ T~ -80~ the label experiences an increasing environmental polarity with increasing temperature in the samples with hydration values higher than about 20 g of water per 100 g of protein.The results are discussed in connection with both conformational substates of the protein and hydration water dynamics.

Azurin-Solvent interaction: an ESR spin labeling investigation

“…Further, for T < 190 K, the value of 2A'~z of Az-3Mal is quite constant, while for Az-Jaa, the same parameter decreases up to 220 K and then slightly increases at T = 230 K. At T > 250 K, instead, 2A'zz drops steeply for both samples. The trend of 2A" of Az-Jaa is slightly different from that reported for hemoglobin-Jaa and lysozyme-Jaa at the same experimental conditions [22,29], where A'~z decreases monotonically with temperature increase, while it is in accordance with values on 3Mal spin labeled human serum albumin studied as a function of hydration [20]. A possible explanation of this behaviour given by the authors is that the increase of 2A'= with temperature should be related to a temperature dependence of the environmental polarity experienced by the label.…”

“…Both labels have been extensively used to study the molecular dynamics of many proteins [17][18][19][20][21] because the spin label can be considered as an additional amino acid residue [22]. In this way, the ESR spectrum of the spin label covalently bound to the protein can reflect either the motion of the macromolecule itself or some residual motion of the label with respect to the whole macromolecule.…”

Solvent modulation of the structural heterogeneity in FeIII myoglobin samples: a low temperature EPR investigation

“…On the other hand, the static CS distribution, characterizing the low temperature myoglobin (Mb) samples, has also been found to be correlated with the properties of the solvent (Di Iorio et al 1991), whose dynamics might be ultimately responsible for the structural arrest of the protein molecules in several different CS (Bizzarri and Cannistraro 1991). Moreover, it has been hypothesized that the hydration water could play a crucial role in determining the dynamics of the protein and the transitions among CS (Doster et al 1986;Singh et al 1981;Marzola and Cannistraro 1992). From a spectroscopic point of view, the presence of a CS distribution may result in a broadening of the detected signal.…”

Rotational dynamics of Di-tert-butyl-nitroxide in normal and supercooled water: an electron paramagnetic resonance study

“…Indeed, a spin probe in water may directly be engaged in the formation of hydrogen bonds; the most evident effect being the variation of its magnetic parameters, like the g and A tensor components [7]. The temperature dependence of the hyperfine coupling tensor (in particular its component along the principal molecular axis) has been, in fact, used [8,9] to show the hydrogen bonding effects on the EPR spectra characteristic of spin labeled proteins.…”