Molecular Interactions between Various Model Cell Membranes and Membrane Active Peptides Studied by Sum Frequency Generation Vibrational Spectroscopy.

摘要

Since the use of native cell membranes for biophysical studies is difficult, membrane mimetics are often used. However, if the model membrane is too simple, it may not be able to provide physiologically meaningful information. As a result, it is important to move toward models that are more similar to native cell membranes in order to study at an environment that is more relevant to physiological conditions. In this thesis work, we utilized sum frequency generation vibrational spectroscopy (SFG) to study how peptides interact with model membranes representing three different cell membrane systems.The mammalian plasma cell membrane was modeled using a solid supported lipid bilayer prepared with a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC):cholesterol mixture. We compared how the antimicrobial peptide (AMP) LL-37 interacts with this bilayer and with a pure POPC bilayer. It was found that the addition of cholesterol inhibited the ability of LL-37 peptide to interact with the phospholipid bilayers. Native bacterial plasma cell membranes were modeled by using bilayers of 1,2-dipalmitoyl-d62-sn-glycero-3-phosphoglycerol (dDPPG)-E. coli polar lipid extract. The interactions of selected peptides with these bilayers and those containing dDPPG-1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) were compared. The use of asymmetric lipid bilayers was able to show that the more complicated interaction mechanisms, such as interaction kinetics, can be studied with the E. coli polar lipid extract and were not easily observed in the POPG lipid system.The bacterial outer cell membrane was modeled using dDPPG-Kdo2 Lipid A and dDPPE:dDPPG(3:1)-Lipid A from Salmonella minnesota R595 bilayers. We compared the interaction of isotope-labeled ovispirin-1 peptides with these membranes and with one or two-component phospholipid bilayers. Because the peptide interacted similarly in systems that primarily differed in the number of sugars extending past the head group region, it was determined that there is no effect on peptide interactions with lipid A with zero or two sugars extending “outside” of the cell.With the knowledge obtained about peptide activity at more realistic bilayers, future studies focusing on predicting antimicrobial effectiveness or designing new antimicrobial molecules will be more accurate and progress more quickly compared to studies utilizing simple model bilayers.