Sensing and Characterizing Interactions with Lipid Membranes
Open Access
- Author:
- Sun, Simou
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- November 30, 2018
- Committee Members:
- Paul S Cremer, Dissertation Advisor/Co-Advisor
Paul S Cremer, Committee Chair/Co-Chair
Philip C Bevilacqua, Committee Member
John H Golbeck, Committee Member
Craig Eugene Cameron, Outside Member - Keywords:
- Lipid Membrane
Biosensor
Physical Chemistry - Abstract:
- Herein, interactions between lipid membranes and physiologically important species, from divalent cations to viral proteins, are sensed and characterized in model membrane systems. By applying vibrational sum frequency generation spectroscopy (VSFS), we show that Ca2+, Mg2+ and Zn2+ bind to phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) in different binding modes, which lead to distinct effects on lipid headgroup orientation and membrane chemical and physical properties. For example, Ca2+-PI(4,5)P2 interactions inhibit protein binding to the lipid, however, Mg2+ can hardly do so. Also, Zn2+ induces lipid domain formation and lipid monolayer phase transition more easily than both Ca2+ and Mg2+. Next, by means of pH modulation fluorescence sensing assay, we demonstrate that the commonly consumed small molecule drug, ibuprofen, interacts with the lipid membrane in three consecutive steps. In each step, the drug has distinct influence on the biophysical properties of the membrane. Further, the interactions between lipid membranes and antimicrobial peptides, viral proteins are studied with the sensing assay. We find that favorable like-charge pairing is formed between nonaarginine (R9) peptides. As such, R9 is able to bind to lipid membranes more strongly and cooperatively than nonalysine (K9), which explains at the molecular level why arginine-rich peptides are better antimicrobial agents than lysine-rich peptides. Also, we are able to identify a new phosphatidylinositide binding site on poliovirus 3C protein, which also acts as the viral RNA binding site. By correlating the fluorescence signal change in the pH modulation sensing assay with the change of membrane surface potential, a mathematic model was built to calculate the surface coverage of divalent cations when binding to negatively charged lipid membranes. As such, we can report accurate binding stoichiometry between Ca2+, Mg2+, Zn2+ and three different anionic lipids. Another aspect of this work is to understand the interactions between PI(4,5)P2 supported lipid bilayers (SLBs) and the solid support, as well as the interleaflet distribution of PI(4,5)P2s in the SLB. We developed a novel analytical assay to separate the two leaflets of a SLB at ambient condition. In this way, we characterized the time-dependent PI(4,5)P2 distribution in the SLBs by directly demonstrating defect-mediated PI(4,5)P2 flipping. Also, we reveal that the strong interaction between PI(4,5)P2 and the underlying glass substrate is due to water-mediated hydrogen bonding.