Abstract
Characterizing the segmental dynamics of proteins, and intrinsically disordered proteins in particular, is a challenge in biophysics. In this study, by combining data from broadband dielectric spectroscopy (BDS) and both depolarized (DDLS) and polarized (PDLS) dynamic light scattering, we were able to determine the dynamics of a small peptide [ε-poly(lysine)] in water solutions in two different conformations (pure β-sheet at pH = 10 and a more disordered conformation at pH = 7). We found that the segmental (α-) relaxation, as probed by DDLS, is faster in the disordered state than in the folded conformation. The water dynamics, as detected by BDS, is also faster in the disordered state. In addition, the combination of BDS and DDLS results allows us to confirm the molecular origin of water-related processes observed by BDS. Finally, we discuss the origin of two slow processes (A and B processes) detected by DDLS and PDLS in both conformations and usually observed in other types of water solutions. For fully homogeneous ε-PLL solutions at pH = 10, the A-DLS process is assigned to the diffusion of individual β-sheets. The combination of both techniques opens a route for understanding the dynamics of peptides and other biological solutions.
Highlights
San Sebastian, Spain † Electronic supplementary information (ESI) available: Relaxation strength versus water concentration, normalized DDLS electric field correlation function for e-PLL solution at pH = 10, Intensity correlation function in VV geometry for water
By combining data from broadband dielectric spectroscopy (BDS) and both depolarized (DDLS) and polarized (PDLS) dynamic light scattering, we were able to determine the dynamics of a small peptide [e-poly(lysine)] in water solutions in two different conformations
We found that the segmental (a-) relaxation, as probed by DDLS, is faster in the disordered state than in the folded conformation
Summary
In well-folded proteins (for instance, globular proteins), water plays an important role in biological activity, and it has been proposed that water determines their structures and dynamics.[6] There is a remarkable coupling between the motions of a solvent and a solute,[7,8,9] and this seems to be valid for IDS proteins[10,11,12] as well as non-biological solutions.[13,14,15]
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