Protein interactions with water, co-solvents, ionic liquids and molecular crowding compounds

Obviously, the molecular environment of a protein is essential for its function. Not only water but many co-solutes and co-solvents play an important role for the integrity and activity of each protein. Therefore, we study the interactions between proteins and solvent molecules and we address their influence on protein structures and binding properties. Ionic liquid compounds are investigated as to their impact on the stability of proteins as well as on directing enzyme activities and specificities. The solvent environment in a living cell is modelled in our studies by "molecular crowding" compounds which enable us to study the kinetics of protein interactions in solvents which are not homogeneous on the molecular level. These studies are pursued within the framework of the Research Department Interfacial Systems Chemistry (IFSC) and the Excellence Initiative RUHR EXPLORES SOLVATION (RESOLV).

Molecular mechanisms of large GTP binding proteins

Expression of human Guanylate Binding Protein 1 (hGBP1) is strongly induced by interferons and other cytokines and it plays a role in immune response to viral and bacterial invasion. It belongs to the family of large GTP binding proteins and we have solved the crystal structure of this dynamin-related protein. We have found a relationship between GTP hydrolysis and assembly to a hGBP1 homo-tetramer. Thereby, a shape of the protein complex is generated which could be complementary to curved membranes. Our research project aims at defining the quantitative relationship between turn-over of GTP by hGBP1 and structural changes possibly leading to force generation used for membrane shaping or essential for cellular localisation and for selection of subcellular compartments. Transient kinetic studies are employed to elucidate the coupling of enzymatic processes in the course of GTP and GDP hydrolysis and the structural changes. Financial support comes from Deutsche Forschungsgemeinschaft and from the Initial Training Network (Marie Curie Actions) TRANSPOL within the 7th EU framework programme.

Cellular signal transduction mediated by protein-protein interactions

Cellular signal transduction is achieved by coordinated protein/protein interaction. Linear and cross wiring is realized, in part, by the formation of multi-protein complexes where competing and synergistic processes play an important role in balancing between many possible responses leading to the desired biological effect. Ras and the effector Raf translate mitogenic stimuli to the activation of a kinase cascade leading to cell proliferation whereas Ras and the effector Nore1A together with other proteins represent the gate to pathways resulting in growth arrest and programmed cell death. Our project aims at the analysis of the structure and the dynamic changes of the multi-protein complexes involved and at understanding the molecular mechanism of differentiation between multiple Ras pathways. In this context we also investigate the inhibitory potential of designed, small compounds with the aim to create a specific drug. This research work is conducted with the help of cooperations and financial support within the Sonderforschungsbereichs 642 and the Protein Research Departments as well as within the excellence initiative PROTEIN INTERACTIONS: From molecular mechanisms to cellular functions and applications.

More specifically we address the following issues:

* Thermodynamic characterisation of protein complex formation

* Stabilisation of proteins by interaction with ionic liquid compounds

* Characterisation of multi-protein complexes in Ras signalling

* Kinetic analysis of protein interactions

* Impact of molecular crowding agents on protein complex formation

* Structural Investigation of protein complexes

* Mechanisms of enzyme catalysed GTP-hydrolysis

* Self assembly of large GTP-binding proteins

* Identification of cellular interaction partners of hGBP1

* Defining protein complex contact areas and mutational analysis