Structure and stability of protein complexes in solution and the gas phase

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Most biological processes, including the immune response, cell-cell communication, inflammation and bacterial and viral infections, involve the association of biomolecules to form specific, non-covalent complexes. The structure and stability of these complexes are determined by the concerted action of many forces (e.g. hydrogen bonds, ionic and van der Waals interactions) between binding partners and from the displacement and reorganization of solvent molecules associated with the solvent shell of the binding partners. An understanding of these forces and the structures they lead to is essential to a complete understanding of biological processes. Research in our laboratory focuses on the development and application of mass spectrometry (MS)-based techniques to detect specific, non-covalent protein complexes (e.g. protein-ligand and multi-protein complexes) in vitro and to characterize their structure and stability in solution and the gas phase. This proposal describes the development of novel experimental methodologies, based on the electrospray ionization (ES)-MS technique, to quantify the kinetic and thermodynamic parameters for non-covalent protein interactions in solution. Specifically, we will develop a direct and sensitive ES-MS approach to quantify the thermodynamic parameters for protein interactions with macromolecules (e.g. proteins and other biopolymers). We will also develop a new method, based on the temperature-jump relaxation approach and ES-MS, to quantify the kinetic parameters for non-covalent protein interactions. The kinetic and thermodynamic data available from these and other methods will allow us to develop a more detailed picture of the structure-function relationships that underlie protein recognition in solution. We will also explore the structure of desolvated non-covalent protein complexes using infrared multiphoton dissociation (IRMPD) spectroscopy. In particular, we will assess the ability of this technique to probe the nature of intermolecular interactions within the gaseous protein complexes. From a comparison of the interactions identified in solution in the gas phase, new insights into the role of solvent in biological recognition will be gained.