Petia Vlahovska1
Northwestern University1
A lipid bilayer is the main component of the membranes that envelope cells and cellular organelles. While the fluidity of the bilayer is known to control lateral mobility of embedded biomolecules, its importance in membrane shape transformations is less appreciated. In this talk, I will discuss the significant role played by membrane viscosity in the bending dynamics of highly-curved structures such as liposomes and sub-cellular organelles. We extend the model of Seifert and Langer [Europhys. Lett, 1993] for the dynamics of a planar viscous bilayer to a quasi-spherical vesicle. The theory predicts a slower relaxation rate, ~q^4, for a spherical harmonic mode q, a drastic change from the classic result ~q^3. Flickering spectroscopy, which is the analysis of experimentally recorded thermally-driven shape fluctuations of giant vesicles (GUVs), confirm the theoretical results in the case of phospholipid/cholesterol mixtures and, for the first time, demonstrate that membrane viscosity slows down bilayer undulation dynamics giving the appearance of an effectively stiffer membrane. For scattering techniques such as Neutron Spin Echo, the theory predicts an anomalous diffusion exponent of 1/2 governing the Dynamic Structure Factor instead of the commonly used 2/3 [Zilman and Granek, Phys. Rev. Lett. (1996)]. Furthermore, we extend the theory to viscoelastic membranes motivated by the flickering dynamics of block-copolymer vesicles and recent electrodeformation experiments that show a two-time scales response, consistent with Kelvin-Voigt viscoelastic material, in the transient ellipsoidal deformation induced by an applied uniform AC electric field of DMPC vesicles near the melting transition.<br/><br/>This research was supported by NIGMS award 1R01GM140461