Liquid-liquid phase separation and crystallization in protein solutions induced by multivalent metal ions

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Liquid-liquid phase separation (LLPS) in protein solutions (i.e. the separation into two liquid phases with low and high protein concentration, respectively) is a crucial phenomenon for protein crystallization as well as protein-association related diseases, such as sickle cell anemia and cataracts. However, the physical mechanisms on the condition of LLPS and its effect on subsequent protein crystallization are still poorly understood. In this proposal, we will undertake a comprehensive study of protein solutions in the presence of multivalent metal ions, where a reentrant condensation phase behavior and LLPS have been observed recently in our group. Our aim is to explore the fundamental mechanisms as well as the key parameters behind of this phenomenon on a molecular level and finally to control the phase behavior of protein solutions. The following questions will be addressed: (a) What is the effective protein-protein interaction potential when LLPS occurs? (b) What are the key parameters determining the phase behavior of protein solutions (nature and concentration of salt, pH, T, …)? (c) What are the differences and similarities between LLPS induced by multivalent ions vs polymer (PEG)? A set of complementary experimental techniques including small-angle scattering (SAXS, SANS), static/dynamic light scattering (SLS/DLS), and spectroscopy (FTIR, UV-vis and circular dichroism) will be used to address the different issues in these complex systems.