Hierarchical molecular dynamics of bovine serum albumin in concentrated aqueous solution below and above thermal denaturation

Abstract

The dynamics of proteins in solution is a complex and hierarchical process, affected by the aqueous environment as well as temperature. We present a comprehensive study on nanosecond time and nanometer length scales below, at, and above the denaturation temperature Td. Our experimental data evidence dynamical processes in protein solutions on three distinct time scales. We suggest a consistent physical picture of hierarchical protein dynamics: (i) self-diffusion of the entire protein molecule is confirmed to agree with colloid theory for all temperatures where the protein is in its native conformational state. At higher temperatures T > Td, the self-diffusion is strongly obstructed by cross-linking or entanglement. (ii) The amplitude of backbone fluctuations grows with increasing T, and a transition in its dynamics is observed above Td. (iii) The number of mobile side-chains increases sharply at Td while their average dynamics exhibits only little variations. The combination of quasi-elastic neutron scattering and the presented analytical framework provides a detailed microscopic picture of the protein molecular dynamics in solution, thereby reflecting the changes of macroscopic properties such as cluster formation and gelation.

Dynamics of proteins in solution

“…The authors identified one component with the translation and rotation of the entire protein, after finding it quantitatively consistent with theories of effective colloidal hard spheres, for all temperatures where the protein is in its native conformational state. Above the denaturation temperature T d , the corresponding diffusion coefficient was found to drop, consistent with the result by Hennig et al (2012), indicating that the motion of the entire macromolecule is strongly obstructed by cross-linking or entanglement (Grimaldo et al, 2015a). The two remaining processes were associated with internal dynamics and interpreted in terms of a model of two switching diffusive states.…”

“…Depending on data statistics, simultaneous fitting of several q values can be used to achieve reliable results for the chosen model parameter, as e.g. proven successfully by Grimaldo et al (2015a). We remark that the flexibility to choose the specific form of Γ 1,2 (q) as well as the switching time distributions for τ 1,2 allows to model processes ranging from simple diffusion and Ornstein-Uhlenbeck processes to continuous time random walks (Roosen-Runge et al, 2016).…”

Picosecond to nanosecond dynamics provide a source of conformational entropy for protein folding

“…ref. 47 and references therein). This demonstrates that internal diffusive motions in proteins on the picosecond timescale are governed by H-bonding and depend weakly on the secondary structure content.…”

Thermally induced conformational changes and protein–protein interactions of bovine serum albumin in aqueous solution under different pH and ionic strengths as revealed by SAXS measurements

“…From the physical point of view, a rise in temperature results in hydrogen bond weakening and strengthening of hydrophobic interactions, 6 and also in a significant alteration of diffusion and accessibility of protein side-chains. 7 Temperature-induced aggregation is observed for all proteins in their native state: at a certain temperature protein globules start to melt, and the association of unfolded intermediates becomes energetically favorable. Kinetic and energetic aspects of this process, as well as the corresponding structural transitions, are widely investigated using numerous techniques, 8 including small angle X-ray and neutron scattering (SAXS and SANS, respectively), which provide information on the structure and interactions of proteins in solution.…”