Professor Tonya L. Kuhl of the University of California-Davis is supported by the Division of Chemistry to develop advanced analytical techniques, including high resolution synchrotron x-ray reflectivity (XR), grazing incidence diffraction (GID), fluorescent microscopy, and surface force microscopy, for the characterization of the structure of lipid membranes and the quantification of the interaction forces responsible for lipid self organization and membrane formation. A systematic approach will be used to determine the effect of lipid composition, environmental conditions, and the chemistry of the underlying support on the structure of the membranes. The lipid membrane will be placed on a pH-responsive polymer cushion to enable the incorporation of proteins without distorting their structure. Another related thrust is to develop a lipid membrane platform for 2-D protein crystallization.
The overarching aim is to develop robust and easily fabricated biomimetic membrane platforms for fundamental biophysical studies and for the assembly of biochemical sensors that mimic the chemical and physical environment of the cell membranes in a controllable manner. Understanding these model systems opens the door for the study of biological membranes which play a crucial role in enabling the proper functions of cells. Students will be trained in the use of advanced photon sources to conduct multidisciplinary research at the interface between chemistry, physics and biology.
Background: Biological membranes are extremely complex, highly organized, responsive thin films composed of a myriad of lipids and proteins. They play a crucial role in mediating cellular function including the transport of materials into and out of the cell, proliferation, signal transduction, and enable the proper function of embedded proteins. Due to their complexity, model systems have primarily been used to study membrane structure and thermodynamic. Despite the large volume of research, the structure and properties of the most basic unit - a single, supported bilayer - remains ambiguous, dependent on preparation method, interplay between the constituent molecules and interaction forces present, and characterization technique used. Further elucidation of the chemical forces and principles of self-organizing lipid systems that are responsible for the membrane’s spatial organization and reorganization due to stimuli has the potential to greatly enhance biomimetic based sensors for a broad array of applications ranging from facilitating fundamental chemical-biophysics research studies to quantifying/screening membrane active pharmaceutical products, developing drug delivery vehicles, inhibiting amyloid formation, or designing antimicrobial agents. Intellectural Merit: The specific goal of this NSF Award was to understand and quantify how surface interactions modify the structure of supported lipid membranes. Our efforts primarily focused on four systems; (1) membranes supported on polyacrylic acid (PAA) polymer cushions, (2) perturbations of membrane structure due to specific protein binding interactions, (3) the structure of membranes cushioned by the incorporation of polyethylene glycol (PEG) functionalized lipids, and (4) measurements of supported membrane-membrane interactions. The PAA cushioned membrane system (1) was demonstrated to provide a robust and tailorable platform to separate membranes from the underlying inorganic support. Protein binding to putative membrane receptors (2) was demonstrated to initiate a new lipid phase and potential mechanism for lipid based outside-in signaling across the membrane. Quantitative comparisons of surface supported lipid bilayers to monolayers and multilamellar lipid films (3) demonstrate that the thickness and head-to-head distance matched well to multilamellar studies validating that single supported membranes are a good approximation of free standing membranes and provide a robust platform for further investigations of more complex membrane systems. Finally, the interaction force-distance profiles between different membrane compositions were measured. Broader Impact: Measurements of the fundamental properties and structure of supported lipid membranes have broad application for development of supported membrane based biosensors and inform the scientific understanding of biological membranes. Outcomes from this award include; development of an easily fabricated polymer cushion system for supporting membranes; a second system to yield micron sized cushioned regions, and discovery of a new, lipid mediated mechanism of signaling across biomembranes. Three graduate students, five undergraduates, and a postdoctoral researcher have worked on portions of this project and were partially supported by this award. Three of the individuals were female and three were from underrepresented minority (URM) groups. An undergraduate researcher was third author on one of the papers. Seven articles have been published detailing the NSF funded research. Three of the papers were in very high impact journals (PNAS, ACS Nano, and Nano Letters). Another paper was the cover article in Langmuir (November 15, 2011). Outreach activities were focused on (1) encouraging URM students to pursue STEM degrees and (2) scientific visits at the 9-12th grade level. Towards these goals, undergraduate student researchers were mentored in the PI’s laboratory. The PI gave seminars each year under the Responsible Conduct of Research (RCR) series specifically on Mentor/Mentee Relationships with an emphasis on retaining URM graduate students. The PI visited primarily URM serving universities CSLA and SJSU to speak to groups of undergraduates majoring in science and engineering about obtaining PhD degrees. The PI hosted high school students and teachers in her laboratory for ½ day visits as part of the Junior Science and Humanities Symposium. The PI initiated and led Biomedical Engineering graduate students to develop engineering demonstrations and visit high school science classes to encourage the visited students to consider engineering and science majors. Information on these activities can be viewed at the following website: http://besaucdavis.wordpress.com/outreach/. A more complete list of activities and the design/improvement of the outreach events is provided at the website: http://besaucdavis.wordpress.com/2010/01/28/besa-outreach-update/#more-823.
