Protein hydration varies with protein crowding and with applied pressure: a sedimentation velocity study

Abstract

We have recently shown, using Derjaguin—Landau—Verwey—Overbeek theory, that the stability of protein solutions can be accounted for primarily in terms of the energy barrier presented by the bound water surrounding the protein, rather than by net repulsive forces. In further work we demonstrated experimentally, using precision densimetry and dynamic light scattering, that the amount of this water bound to proteins varies with temperature. We have now used the analytical ultracentrifuge (AUC) to study possible effects of crowding and applied hydrostatic pressure on water binding and hence on the sedimentation velocity of proteins. We show that whilst self-cancelling of effects minimises changes in the s values, there are predictions, which we are able to confirm experimentally, that both high protein concentration and elevated hydrostatic pressure at levels found in the AUC will lead to effects attributable to additional hydration. It is concluded that protein hydration is, over a range of conditions, a variable rather than a constant quantity. This finding is significant in relation to the stability and formulation of protein solutions.