MIPBPS

The role of multivalent ions in tuning the phase behaviour of protein solutions

01/08/2015 to 31/07/2017

Recent research including the M. Sc. thesis preceding this PhD project has revealed that thermodynamic phenomena such as reentrant condensation (RC), liquid-liquid phase separation (LLPS), crystallisation as well as an atypical lower critical solution temperature (LCST)-type behaviour can be observed in systems consisting of proteins and multivalent salts. The results obtained during the M. Sc. thesis furthermore indicate that the size of the multivalent ions is an important parameter by which the phase behaviour can be tailored.

During the first part of the PhD project presented here, a systematic analysis of the physical mechanisms behind the transitions described above will be performed in different protein-salt systems in order to understand how they are influenced by salt characteristics (e.g. ion size), solvent properties and structural and chemical properties of different proteins. Another question addressed will be how these transitions can be specifically induced and tuned by selecting appropriate parameters such as protein and salt concentrations, temperature and type of salt used. The methods employed will include temperature-dependent UV-Vis spectroscopy, zeta potential measurements, optical microscopy, infrared spectroscopy as well as circular dichroism. Structural features and effective interactions in the protein solutions will be investigated using small-angle scattering and light scattering which will also help optimise protein crystallisation conditions via the characterisation of the structure factor S(q) of the respective systems. The mechanism of the unusual LCST behaviour will be probed with isothermal titration calorimetry.
In the second part of this PhD project, the LCST effect will be exploited in order to create temperature-sensitive, biocompatible protein networks capable of controlled substance release. The temperature dependence of the networks will be brought about by the addition of multivalent salts. The networks will be fabricated by crosslinking proteins using glutaraldehyde. The crosslinking conditions will be optimised systematically with respect to appropriate protein:crosslinker ratios as well as types of proteins and salts.

In conclusion, the goal of the first part of the project will be a systematic characterisation of the thermodynamics behind phase transitions in multiple protein-salt systems. The second part will use the theoretical knowledge obtained in the first part in order to design "smart" materials. Overall, the two parts of the PhD project proposed here will allow to gain fundamental knowledge concerning phase behaviour in protein systems.