SEMINAR: Insights into lipid membrane dynamics: understanding thickness fluctuations through Neutron Spin Echo experiments

Dr Paul Butler, Center for Neutron Research, National Institute for
Standards and Technology (NIST), Gaithersburg, MD, USA

 Thursday August 28th, 15:15-16:00
Auditorium S11, Ørsted Institute, Universitetsparken 5

 Biological membranes are highly complex, self-assembled, two dimensional structures which separates the living cell from its environment and provides a semi-permeable barrier maintaining a delicate balance of substances within and outside the cell.

While early studies viewed the lipidic membrane as a simple support matrix and focused on the inclusions, specially the membrane proteins, there is a growing consensus, supported by theory, simulation and experiment that the lipid membrane actively participates in its function, supporting, and even regulating the activity of the embedded proteins and oligomers.

 In this work we probe the intermediate range dynamics of thickness fluctuations. Such fluctuations have been predicted by, and their features explored through, theoretical and simulation work, but not experimentally observed. They are thought to significantly impact such things as the insertion and functioning of membrane proteins as well as pore formation and cellular exchange. We have used neutron spin echo (NSE) to experimentally observe these fluctuations first in the simplest model systems of pure, fully saturated, phosphocholine unilamellar vesicle (ULV), examining the role of both Tm and chain lengths. We then increase the complexity of our model system to explore the effects of using mixed tail lengths (and mixed Tm). Interestingly we find that the amplitude and relaxation times are independent of chain length in single lipid systems. However, upon mixing a 50/50 ratio of longer and shorter chains we observe a significant enhancement of the fluctuations with temperature above the Tm of the longer chain lipid.

Organizer: Lise Arleth arleth@nbi.ku.dk – Please contact Lise if you want to schedule a meeting with Paul.