8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Wed 711:10-14:00P5.137Exploring protein self-diffusion in crowded solutionsFelix Roosen-Runge, 1 Marcus Hennig, 2 Fajun Zhang, 1 Robert M. J. Jacobs, 3Helmut Schober, 2 Tilo Seydel, 2 and Frank Schreiber 41 Universität Tübingen, Institut für Angewandte Physik, 72076, Tübingen, Germany2 Institute Laue-Langevin, Grenoble, France3 University of Oxford, Oxford, United Kingdom4 Universität Tübingen, Tübingen, GermanyUsing quasi-elastic neutron backscattering, we probe the self-diffusion in aqueous solutions of themodel globular protein bovine serum albumin (BSA) on nanosecond time and nanometer lengthscales. We thereby address fundamental issues of colloid physics applied to soft nanoscale biologicalobjects which are by nature monodisperse in size, but have a non-spherical shape and aninhomogeneous surface charge distribution, both of which are in contradiction with conventionalcolloidal model systems. In particular, the situation of molecular crowding, i. e. high proteinvolume fractions in the solution, challenges the applicability of colloid theory. We present a systematicstudy of the self-diffusion of BSA in aqueous solution as a function of the protein volumefraction. The measured diffusion coefficient D strongly decreases. We discuss the separation ofthe rotational Dr and translational Dt contributions to D. The resulting Dt of the proteins is put inthe context of existing colloidal short-time self-diffusion models of charged and non-charged hardspheres. In combination with well-known results on the long-time diffusive behavior of proteins,the presented results on the short-time self-diffusion invoke a colloidal picture of macromolecularcrowding, thereby suggesting hydrodynamic interactions to contribute considerably to the slowingdownof diffusion in the biological cell. The success of the simple modeling and the experimentalfindings opens the field for future applications of neutron scattering, where inter alia internal proteindynamics can be reliably seperated from global diffusive protein dynamics under crowdingconditions.137