Probing the Intermolecular Interactions of Lactoferrin

In this work the effect of pH and ionic strength on interactions for the globular protein lactoferrin has been studied using static and dynamic light scattering. The interactions were investigated in terms of the second virial coefficient, B2, and the collective diffusion coefficient, Dcoll, at different concentrations of electrolyte. The conditions investigated in this work will serve as a stable point-of-departure from which we will set out, in a controlled way, to explore the phase diagram with the aim to use lactoferrin as a model protein to investigate the role of patchy attractive interactions, i.e. charged groups and hydrophobic groups are unevenly distributed at the protein surface. The charged groups depend strongly on both pH and ionic strength. The overall reproducibility and stability against time are crucial and shown here to be highly satisfactory. From determination of B2 the interactions are found to be, at the investigated pH and ionic strength, overall repulsive and in agreement with computer simulations and preliminary SAXS measurements. However, the collective diffusion coefficient appears to be, under the same conditions, not as repulsive which calls for further measurements and analysis.