Average and dynamic properties of membrane lipids studied by deuterium NMR spectroscopy.
AuthorThurmond, Robin Leroy.
AdvisorBrown, Michael F.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractIf the function of membrane lipids were only to provide a permeability barrier for cells, than a single lipid species such as phosphatidylcholine would suffice since it would maintain the bilayer structure necessary for a membrane. Cells, however, go out of their way to regulate the components of their membranes and therefore there must be some reason for the vast diversity of lipids found even in a single membrane. Modulation of the phospholipid composition could affect both the average and dynamical properties of the entire system. Average properties such as the hydrocarbon thickness, the area per lipid molecule, or the curvature stress across the bilayer could play a role in membrane function and therefore it is important to understand how different lipid components influence these physical properties. The goal of this work has been to understand how different lipid components such as changes in headgroup and acyl chain unsaturation as well as cholesterol and bile salts affect the properties and structure of membranes through the use of deuterium nuclear magnetic resonance spectroscopy (²H NMR). Saturated and unsaturated phosphatidylethanolamines and phosphatidylcholines have been studied in the low temperature, lamellar liquid-crystalline, and reversed hexagonal phases. Measurements have been made of the average projected acyl chain length, the average area per molecule, the radius of curvature in hexagonal phases, and various relaxation rates. These studies were not only carried out on single component synthetic systems but also mixture of lipids and even native membranes through the use of a deuterated probe molecule. It was concluded that different lipids modulate different properties of membranes. Phosphatidylcholines along with monounsaturation keep the membranes in a fluid state whereas the presence of phosphatidylethanolamines and polyunsaturation increase the curvature stress in the monolayers. With this in mind experiments were carried out to determine how the average properties of membranes relate to membrane protein function. These studies show the promise of combining physical chemical measurements of membrane properties with biochemical measures of protein function. Such studies will allow for a better understanding of membrane function and the role lipid diversity plays in such functions.