Dynamics of Protein and its Hydration Water: Neutron Scattering Studies on Fully Deuterated GFP

Abstract

We present a detailed analysis of the picosecond-to-nanosecond motions of green fluorescent protein (GFP) and its hydration water using neutron scattering spectroscopy and hydrogen/deuterium contrast. The analysis reveals that hydration water suppresses protein motions at lower temperatures (<~ 200 K), and facilitates protein dynamics at high temperatures. Experimental data demonstrate that the hydration water is harmonic at temperatures <~ 180-190 K and is not affected by the proteins' methyl group rotations. The dynamics of the hydration water exhibits changes at ~ 180-190 K that we ascribe to the glass transition in the hydrated protein. Our results confirm significant differences in the dynamics of protein and its hydration water at high temperatures: on the picosecond-to-nanosecond timescale, the hydration water exhibits diffusive dynamics, while the protein motions are localized to <~3 Å. The diffusion of the GFP hydration water is similar to the behavior of hydration water previously observed for other proteins. Comparison with other globular proteins (e.g., lysozyme) reveals that on the timescale of 1 ns and at equivalent hydration level, GFP dynamics (mean-square displacements and quasielastic intensity) are of much smaller amplitude. Moreover, the suppression of the protein dynamics by the hydration water at low temperatures appears to be stronger in GFP than in other globular proteins. We ascribe this observation to the barrellike structure of GFP.

Hydration water and peptide dynamics – two sides of a coin. A neutron scattering and adiabatic calorimetry study at low hydration and cryogenic temperatures

“…69 The same conclusions were drawn from a neutron scattering study of D 2 O hydrated hydrogenated GFP (green fluorescent protein) and a H 2 O hydrated sample of fully deuterated GFP. 9 The values obtained for the proton mobility as a function of temperature for the two hydrated samples ( Fig. 1 and 2) show three temperature dependence regions, in accordance with previous studies.…”

“…1 and 2) show three temperature dependence regions, in accordance with previous studies. 9,11,13 For the nominally dry peptide we did not observe a break in the temperature trend of hu 2 i values up to B240 K, as expected (Fig. 1, inset).…”

“…The change in slope of the temperature dependence of hydrated protein's mean-square displacement around 220 K has been extensively studied, 9,11,13,23,24,67,68 as this transition is connected to protein function and vanishes in the absence of hydration. It has been proposed that the dynamical crossover around 220 K could be associated with a large scale structural change in hydrogen bond connectivity.…”

“…The steeper increase above 220-230 K is usually correlated with the so called dynamic transition, reflecting the increase in internal rotation and translation dynamics. 9,12,13,23,24,28,32 The hu 2 i values for a nominally dry sample (Fig. 1, inset) shows linear temperature dependence up to about 240 K, and a deviation from linearity above this temperature.…”

“…Nevertheless, many aspects regarding its particular structure near the surface and inside biological macromolecules as well as its link to biological function are still under discussion. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Proteins are known to have a ''limiting hydration'' necessary for function, and thus there must exist a link between hydration and protein functional properties.…”