Inelastic light scattering studies of biological macromolecular solutions and virus crystals

Abstract

In this study, Brillouin light scattering is used as a tool to explore the elastic and viscoelastic properties of different macromolecular systems. Specifically, we explore two common macromolecular systems: aqueous solutions and crystals. By performing experiments on these different systems, we are able to explore the evolution of the properties of interest in three distinct regimes. By performing experiments on aqueous solutions, we are able to explore the dilute regime, wherein solute molecules may be treated as non-interacting particles, and the semi-dilute regime, where intermolecular interactions cannot be neglected. Finally, performing experiments on macromolecular crystals allows us to observe the elastic properties of macromolecules in the solid state. The effects of macromolecular crowding have been extensively studied by various experimental techniques. Such works have demonstrated a significant amount of binding of solvent to the hydration shells of such crowders, drastically reducing the available free volume. In this work, Brillouin light scattering experiments were performed on aqueous solutions of Ficoll 70 and Ficoll 400 with concentrations ranging from 1 wt% to 35 wt% and Bovine Serum Albumin with concentrations of 1 wt% to 27 wt%. By examining the evolution of longitudinal Brillouin peak parameters with solute concentration, we calculated viscoelastic properties, including hypersound velocity, adiabatic bulk modulus and compressibility, apparent viscosity, and hypersound attenuation. Existing theory could only capture trends in this evolution up to a threshold concentration due to the neglect of intermolecular interactions. As such, the addition of a quadratic term was incorporated to account for intermolecular interactions between solute molecules. In Ficoll solutions, evidence of a central mode, which is due to relaxation of solvent in the polymer hydration shell, was observed. In recent years, there has been a growing amount of interest in exploration of the elastic properties of crystalline macromolecular structures. Such properties of virus crystals, however, are still hardly known. In the present work, crystals of satellite tobacco mosaic virus were grown using hang drop vapour diffusion techniques. Crystal clusters grown were subsequently used in Brillouin light scattering experiments. Peaks in Brillouin spectra were determined to be due to longitudinal bulk modes, and the parameters of these peaks were used to approximate hypersound velocity and attenuation within the crystals.