The knowledge of interactions between proteins in crowded mixtures, as they exist in the interior of living cells, is essential since they ultimately determine their stability, phase behavior, solution structure and dynamics. As a first step on our way to establish a well-defined model cytosol with a complete experimental description of the effective interactions and the resulting solution structure and thermodynamic stability, we need to identify individual proteins that differ in size and charge and are suitable components for our generic cell cytosol.

One potential candidate is calbindin D_9k, a monomeric calcium-binding protein of the S100 family of the calmodulin-related proteins, involved in Ca²⁺ buffering and in trans-cellular transport of Ca²⁺ ions. We investigate the solution structure of calbindin D_9k using SAXS and quantify the protein-protein interactions through second virial coefficients as a function of the calcium binding state (holo and apo) and the screening conditions, both experimentally and via Monte Carlo computer simulations. In a next step we study the interactions/aggregation behaviour of calbindin with the oppositely charged lysozyme.

People:Najet Mahmoudi, Coralie Pasquier, Mikael Lund, Sara Snogerup Linse, Jeppe Lyngsø and Jan Skov Pedersen (Aarhus University), Anna Stradner.

Contact person: Anna Stradner