Dynamics of lipid bilayers studied by neutron spin echo spectroscopy

by Prof. Michihiro Nagao

National Institute of Standards and Technology (NIST) Center for Neutron Research & Dept. of Materials Science and Engineering, Uni. of Maryland & Dept. of Physics and Astronomy, Uni. of Delaware

at Biological and soft-matter physics

Thu, 23 Dec 2021, 14:10
Zoom recording link provided

Abstract

Lipid bilayers are considered model biological membranes, which are a unique and dynamic platform of various biological functions. Studies on static and dynamic structures of lipid bilayers have been performed using various techniques, among which neutron scattering techniques are one of the best suited techniques to access molecular to molecular aggregate length scales and their dynamics. Our group has studied dynamics of lipid bilayers by employing neutron spin echo (NSE) spectroscopy, which covers the length and time scales of sub Å to several 10 nm and ps to several 100 ns, to understand elastic and viscous properties of lipid bilayers. In the small scattering angle regimes, scattering from membrane assemblies is observed, where we see the collective membrane fluctuations, such as undulation and thickness fluctuations. Undulation fluctuations are controlled by the elastic bending rigidity of the membrane. On the other hand, area compressibility of the membrane drives the thickness fluctuations which are overdamped by both membrane and solvent viscosities. By accessing these dynamics [1], we have developed a methodology to estimate the bending and area compressibility moduli as well as the membrane viscosity through a NSE measurement [2]. Interestingly, these parameters are scaled with the membrane structural parameter, namely area per molecule, in the fluid phase of mixed saturated lipid bilayers [3].
To understand the origin of membrane viscosity, we recently measured collective dynamics of lipid acyl tail correlations, where density fluctuations of lipid acyl tails and lipid molecules are accessible in the fluid phase by means of NSE [4]. The time scale of these motions was measured at about 10s of ps and 100s of ps, respectively. By employing the relation between the relaxation time scale of density fluctuations and viscosity in three-dimensional molecular liquids, we estimated the membrane viscosity in the two-dimensional fluid and gel phase lipid bilayers. The values of the membrane viscosity in the fluid phase are about a mean of broadly distributed membrane viscosities reported in literature. We concluded that the molecular origin of the membrane viscosity is the time scale of the lipid molecules rearranging in the membrane.
References:
[1] A.C. Woodka, P.D. Butler, L. Porcar, B. Farago and M. Nagao, Physical Review Letters 2012, 109, 058102.
[2] M. Nagao, E.G. Kelley, R. Ashkar, R. Bradbury and P.D. Butler, Journal of Physical Chemistry Letters 2017, 8, 4679-4684.
[3] E.G. Kelley, P.D. Butler, R. Ashkar, R. Bradbury and M. Nagao, Proceedings of National Academy of Science U.S.A. 2020, 117, 23365.
[4] M. Nagao, E.G. Kelley, A. Faraone, M. Saito, Y. Yoda, M. Kurokuzu, S. Takata, M. Seto and P.D. Butler, Physical Review Letters 2021, 127, 078102.

Recording can be watched on:
https://us02web.zoom.us/rec/share/PIrNTk51rZ5EPNyBJu2eyVJ2P50DpAw74kJIJprSxonUlNmcOSLq9-jwQeMYWHrv.dbxAt_6oIXw5dTFj

Created on 29-11-2021 by Granek, Rony (rgranek)
Updaded on 23-12-2021 by Granek, Rony (rgranek)