What can we learn about complex formation by combining thermophoresis with QENS?

Molecular recognition via protein–ligand interactions is of fundamental importance to most processes occurring within living organisms. Structural fluctuations and conformational motions of proteins are essential for the binding of ligands and other interaction partners. This binding process is governed by equilibrium thermodynamics and the minimization of the free energy ΔG for the whole system. Also the thermophoresis, the diffusion in a temperature gradient, is sensitive to the complex formation. This effect has been used intensively to gain detailed information on binding dynamics, but the physicochemical processes are still unclear [1]. The strong sensitivity of proteins and other water soluble biomolecules to the temperature gradient is probably caused by a change in the hydration layer, which is influenced by subtle conformation changes induced by the binding of the ligand molecule. We want to correlate the information about the hydration layer obtained in thermophoresis experiments with changes of structural fluctuations and conformational motions measured by quasi-elastic incoherent neutron scattering (QENS) and isothermal titration calorimetry (ITC). As model system we want to study streptavidin-biotin. Streptavidin is a 58.8 kDa protein with an extremely high affinity for the ligand biotin (also known as vitamin B7 or vitamin H). The thermodiffusion is investigated by infrared thermal diffusion forced Rayleigh scattering (IR-TDFRS) [2].

[1] M. Jerabek-Willemsen, T. André, W. Wanner, H. M. Roth, S. Duhr, P. Baaske, D. Breitsprecher, J. Mol. Struct. 2014, 1077, 101-113.
[2] S. Wiegand, H. Ning, H. Kriegs, J. Phys. Chem. B 2007, 111, 14169-14174.