Polymer-Lipid Particles investigated by Magnetic Resonance Spectroscopy

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Project Summary/Abstract Membrane proteins represent approximately 30% of all known proteins but only approximately 1% of all solved protein structures. Despite recent advances in methods for membrane protein structural biology, knowledge about this important class of proteins lags behind their soluble counterparts. Membrane proteins are critical to numerous aspects of health, ranging from regulation cellular function and transport into and out of the cell, through to viral infections which use membrane proteins as part of the infection cycle. Understanding the structure of membrane proteins can be critical to disrupting such viral infections, and can also lead to the development of effective antiviral therapies. In almost 90% of newly developed and approved therapeutics, protein structural information was used to guide the development of the therapeutic molecules. Due to the limited and incomplete structural information on membrane bound proteins, the development of therapeutics and treatments that target membrane bound proteins is limited. A significant contribution to the challenges in elucidating membrane protein structures is the lack of robust and appropriate lipid membrane mimetics. Existing membrane mimetics introduce notable challenges that limit membrane protein structural determination. These challenges range from highly curved micelles which may not represent the essentially flat lipid bilayer, lack of compatibility with many lipids for bicelles, large sizes of vesicles which introduces anisotropy, cost and potential background signal from membrane scaffold proteins, and lack of control over polymer structure and the presence of aromatic groups on several existing nanodisc forming polymers. This highlights an urgent need to develop lipid membrane mimetics which both provide a good approximation to the native lipid bilayer in terms of both structure and curvature, while also facilitating structural analysis of the membrane protein embedded in the mimetic. Yet polymer structure-function relationships are not well established for polymers that interact with lipids and membrane proteins. This project will use modern controlled polymer chemistry tools, to create a new class of polymers that will self-assemble with lipids. These self assembled polymer-lipid systems will form well defined discs on the order of 10s of nanometers, giving lipid membrane mimetics suitable for the analysis of many membrane proteins. The advanced polymer chemistry techniques will enable fine tuning of polymer’s length, charges, and hydrophobicity. Polymers will also be modified with spin-labels for electron paramagnetic resonance spectroscopy, a magnetic resonance method. The magnetic resonance spectroscopic methods will be used on polymers, lipids and membrane proteins modified with appropriate spin labels, providing insights into the local dynamics and proximities of the self assembled polymer-lipid and polymer-lipid-membrane protein complexes. The information regarding the structure and dynamics of the self-assembled complexes across the diverse range of polymer functionality and structures used will give important insights into how polymer structure impacts its interactions and assembly with biological molecules. These insights can be used to guide the design of polymers for robust lipid membrane mimetics. Training and mentoring of undergraduate students as well as a graduate assistant will be a core feature of the proposed project. A diverse team of students will work on all aspects of the project, gaining skills from the fundamental polymer chemistry, magnetic resonance spectroscopy to membrane protein biophysics. Undergraduate students will be integrated fully into the projects, along with the graduate student, gaining skills in this field at the interface of materials science and biophysics. Beyond core scientific training, students will gain written and oral communication skills disseminating the results of the research.