Hydrodynamic radius coincides with the slip plane position in the electrokinetic behavior of lysozyme.

ABSTRACT: The zeta potential (?) is the effective charge energy of a solvated protein, describing the magnitude of electrostatic interactions in solution. It is commonly used in the assessment of adsorption processes and dispersion stability. Predicting ? from molecular structure would be useful to the structure-based molecular design of drugs, proteins, and other molecules that hold charge-dependent function while remaining suspended in solution. One challenge in predicting ? is identifying the location of the slip plane (XSP ), a distance from the protein surface where ? is theoretically defined. This study tests the hypothesis that the XSP can be estimated by the Stokes-Einstein hydrodynamic radius (Rh ), using globular hen egg white lysozyme as a model system. Although the XSP and Rh differ in their theoretical definitions, with the XSP being the position of the ? during electrokinetic phenomena (e.g., electrophoresis) and the Rh being a radius pertaining to the edge of solvation during diffusion, they both represent the point where water and ions no longer adhere to a molecule. This work identifies the limited range of ionic strengths in which the XSP can be determined using diffusivity measurements and the Stokes-Einstein equation. In addition, a computational protocol is developed for determining the ? from a protein crystal structure. At low ionic strengths, a hyperdiffusivity regime exists, requiring direct measurement of electrophoretic mobility to determine ?. This work, therefore, supports a basic tenant of EDL theory that the electric double layer during diffusion and electrophoresis are equivalent in the Stokes-Einstein regime.

SUBMITTER: Grisham DR 

PROVIDER: S-EPMC6656557 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature