Speaker: Ralf Biehl, Jülich Centre for Neutron Science (JCNS), Germany.

Title: Domain Motions: Protein Dynamics seen by Neutron Spinecho Spectroscopy

Abstract

Proteins are the molecular machinery of life. As nanomachines of metabolism, they are in every cell of our body tirelessly active, transport, synthesize, divide and transform substances. Neutron Spin Echo Spectroscopy (NSE) is a versatile tool to investigate functional collective dynamics as large-scale movements on the 1 to 200 nanosecond timescale on different length scales with the ability to determine the relaxation time and amplitude of the motions. In combination with other inelastic NS techniques, SANS/SAXS and NMR structure and function of proteins can be enlightened on the natural size- and timescale of these macromolecules. SAS and NSE use coherent scattering and observe the ensemble structure and correlations within the ensemble. To separate domain motions the collective motions between proteins must be considered. After an introduction to the techniques and theory, I will present several examples showing proteins of different structure, resulting domain motions and relation to function. Phosphoglycerate kinase shows a clear hinge motion related to function. By thermal unfolding of Ribonuclease A the transition of a rigid protein to an unfolded chain with 4 disulfide bonds can be observed. Chain dynamics is dominated by internal friction and the activation energy can be retrieved. Immunoglobulin present a dynamics due to the short linkers connecting the Fc with the Fab fragment. Analysis by a Ornstein-Uhlenbeck process result in the determination of friction and spring constants. Overall neutron scattering is shown to be a unique tool to examine the micromechanics of proteins on the length scale of domains with the ability to examine forces and friction.

Bio

 Ralf Biehl received his PhD in Physics from the University Mainz, Germany in 2002 doing optical shear rheology on colloids. After his postdoctoral time as instrument scientist at the NSE instrument in Jülich he became staff scientist at JCNS in Jülich in 2008. From 2014-2019 he was member, later chair, of the subcommittee Biology at ILL. His general interest is to identify functional domain motion and characterize timescale and amplitudes by combining neutron scattering methods like NSE with other complementary biophysical methods.