Electron Spin Relaxation in Model Membranes

Abstract: This project is aimed at the study of properties of membrane proteins that underlie importantbiomedical processes and are implicated in health disorders and how they interact with their membraneenvironments. By means of the latest one and two dimensional electron-spin resonance (ESR) methodologies,including Pulse-Dipolar ESR (PDS), multifrequency ESR, and Two-Dimensional Electron-Electron DoubleResonances (2D-ELDOR), as well as site-directed nitroxide spin-labeling methods, we will directly observesignificant protein functional changes and in parallel experiments, observe the concomitant changes occurringin the dynamic structure of the lipid bilayers. This ability to accurately characterize both membrane andmembrane protein is an innovative approach toward understanding on the role of membrane-proteininteractions affecting the protein's function. Specific projects include the following. First, we will advance ourstudy of the mechanism of viral membrane fusion, based on our previous success in detecting the membraneordering effect of influenza and HIV glycoprotein fusion peptides (FP). We will extend this study to the structureof their FP-transmembrane domain complex in membranes and to quantification of the induced microdomain,plus we shall extend the study to SARS and gamete membrane fusogens. In the second project, the tauprotein, which plays an important role in neurodegeneration, will be studied. We have shown how tau interactswith membranes and adopts different conformations in response to the curvature of liposomes, so we plan tostudy the interaction between tau and microtubules, which directly addresses its functional and pathologicalroles in neurodegenerative diseases. The third project will focus on the structure of asymmetric membranes,which are crucial for cell function. We will investigate how both membrane leaflets interact with each other, andhow the changes in the composition of one leaflet affect ordering and fluidity of the other, as well as how themodel peptide gramicidin changes their structure and facilitates lipid flip-flop. In the fourth project, we will studythe influenza A M1 and M2 matrix proteins, which are related to viral infectivity and proliferation. We previouslyshowed the oligomerization of M2 TMD in membrane is a two-step process and the stoichiometry is affected byligand binding. We will focus on the effect of lipid composition on the M1 oligomerization. We will also study thestructure of the M1-M2 complex in membranes. In the fifth project, our ESR studies on the mechanism oftransmembrane signaling in bacterial chemoreceptors will be continued and extended. We will 1) characterizethe lipid dependence of the piston motion exhibited by chemoreceptors, 2) examine the effect of receptoroligomerization state and conformation on lipid structure, and 3) probe the interactions of the chemoreceptorsensing domain relative to the lipid bilayer. All these studies will involve extensive collaborations with leadingresearch groups. Possible clinical applications include detection of membrane changes during immuneresponse, prevention of viral entry, fertility diseases, neurological disorders, and development of antimicrobials.