(196a) Interpreting the Protein Phase Diagram Via Colloid Physics

The richness of protein phase behavior is widely exploited in protein separations as well as in such applications as formulation of biologics, food processing and structural biology.  Protein solutions can give rise to a variety of dense phases, including crystals, precipitates, gels and concentrated liquids, some of which are equilibrium phases while others are kinetically trapped.  It is a challenge both to classify some phases observed experimentally and, especially, to organize the phase behavior into a rational phase diagram showing the different phases and their relationship to one another.  Partial insights into the structure of the protein phase diagram can be obtained from idealized colloidal models that treat protein molecules as spheres interacting isotropically via fairly weak, short-ranged attraction.  However, these models do not reflect the full richness of experimentally observed behavior, and this presentation will examine further complexity resulting from ansiotropic contributions to the interactions.  Some of these can be elucidated via models of "patchy" colloids, and the significance of the structure of the resulting dense phases and the implications for proteins will be a particular focus of the presentation.