Challenges in Predicting Protein-Protein Interactions from Measurements of Molecular Diffusivity.
Dynamic light scattering can be used to measure the diffusivity of a protein within a formulation. The dependence of molecular diffusivity on protein concentration (traditionally expressed in terms of the interaction parameter kD) is often used to infer whether protein-protein interactions are repulsive or attractive, resulting in solutions that are colloidally stable or unstable, respectively. However, a number of factors unrelated to intermolecular forces can also impact protein diffusion, complicating this interpretation. Here, we investigate the influence of multicomponent diffusion in a ternary protein-salt-water system on protein diffusion and kDin the context of Nernst-Planck theory. This analysis demonstrates that large changes in protein diffusivity with protein concentration can result even for hard-sphere systems in the absence of protein-protein interactions. In addition, we show that dynamic light scattering measurements of diffusivity made at low ionic strength cannot be reliably used to detect protein conformational changes. We recommend comparing experimentally determined kDvalues to theoretically predicted excluded-volume contributions, which will allow a more accurate assessment of protein-protein interactions.
Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado.
Lea L
LL
Sorret
Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado.
Madison A
MA
DeWinter
Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado.
Daniel K
DK
Schwartz
Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado. Electronic address: theodore.randolph@colorado.edu.
Theodore W
TW
Randolph
D004058:Diffusion; D008958:Models, Molecular; D025941:Protein Interaction Mapping