Collaborative Research: Lipid Bilayers and Interfacially Active Peptide
INTELLECTUAL MERIT: Interfacially active peptides bind to bilayer membranes and drive the rearrangement of lipids. There are two different outcomes of this interfacial activity, either (1) bilayer destabilization leading to leakage of solutes through the membrane, or (2) peptide translocation without significant solute leakage. However, it is not known which factors determine these two very different outcomes. Because a mechanistic understanding is still lacking, it is not currently possible to predict how a particular peptide will interact with a lipid bilayer. In this proposal, the PIs have selected 19 peptides from within three families: interfacially active peptides, translocating peptides, and membrane inactive peptides. These peptide families have been identified using a high throughput, orthogonal screen of 13,000 peptides. The selected peptides will be characterized in terms of their binding to bilayers, disposition in bilayers, and effects on bilayer electrical properties. Specifically, the PIs will characterize the disposition of peptides from the three families (leakage-inducing, translocating, and inactive) in lipid bilayers using neutron reflectivity and diffraction. In a second line of attack they will characterize the electrical response of supported bilayers to the three families of peptides (leakage-inducing, translocating, and inactive) using electrochemical impedance spectroscopy (EIS). These experiments will be performed at known bound peptide concentrations guided by the outcome of preliminary work.
BROADER IMPACTS: The scientific broader impacts lie in the capacity of this project to identify correlations between the chemical structure of interfacially active peptides and their mode of action. Understanding of these correlations will then permit design of new peptides that may have therapeutic or scientific applications. The project will sponsor student exchanges between Tulane and Johns Hopkins. In particular, a six month visit to Johns Hopkins by a graduate student from Tulane and summer visits by New Orleans high school students and Tulane undergraduates are planned. The intention is to introduce the students from New Orleans to materials science as a discipline, given that there are no materials science departments at the New Orleans universities. The laboratories at both institutions will include undergraduates on the research teams in keeping with long standing practice. The Johns Hopkins group will collaborate with the JHU Women in Science and Engineering program to reach out to female high school students in the Baltimore area in an effort to interest them in careers in science and engineering.
In this program, we have identified a family of 12 residue long peptides that spontaneously translocate across membranes (Marks et al, J. Am. Chem. Soc. (2011) 133:8995-04). The peptides were discovered in an orthogonal high throughput screen by an approach that will be useful outside of this specific area. These peptides function by a mechanism that is very different from that of the well known, highly cationic cell penetrating peptides such as the tat peptide from HIV. The newly discovered translocating peptide family can carry polar cargoes across synthetic bilayers and across cellular membranes. They do this quickly and spontaneously without disrupting the membrane structure. Work under the award has significantly advanced our understanding of translocating peptides, and membrane active peptides in general. This Collaborative work resulted in 13 papers that broadly address the structure and function of membrane active peptides and the extraordinary ability of some peptides to cross membranes. The work may be useful in future drug delivery applications. In the course of this work several graduate students and postdocs were trained in biophysical and materials science techniques, as well as in presentation and speaking skills. Cross-talk between researchers at the Tulane School of Medicine and the Johns Hopkins School of Engineering resulted in significant exposure of Tulane researchers to the principles of materials science, a discipline that is poorly represented in Louisiana.
