Understanding lipid membranes' interactions with small molecules and cholesterol using molecular dynamics computer simulations.
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Cellular membranes are made up of phospholipids, proteins and cholesterol. The packing of components within the membrane gives rise to important biological phenomena. Understanding these interactions is the most critical step towards predicting membrane behavior. In this dissertation, I focus on lipid bilayer interactions with various molecules. At biologically relevant scale, we investigate how phospholipids interact with small molecules like amino acid residues and cholesterol. At field scale, we study the structure and dynamics of lipid molecules as they bind with clay minerals. I utilize molecular dynamics simulation, both equilibrium and biased, at both coarse-grained and atomistic level to study how these interactions impact membrane thermodynamic properties. I first study membrane permeation by evaluating the efficiency of different computational methods to sample the configurational space of various amino acid and lipid membranes. I show that replica exchange umbrella sampling out-performs others because of the algorithm’s ability to sample transition state. Using this method, I calculate cholesterol chemical potential in seven binary lipid membranes. These results demonstrate the sensitivity of the cholesterol chemical potential to the lipid tail unsaturation only if the difference in tail saturation is big, and show that cholesterol has the greatest affinity to saturated PC lipids. These studies provide practical guidance for studying membrane permeation and yield important insight into the thermodynamic properties of lipid bilayer systems. This work will also contribute towards the understanding of cholesterol’s effect of membranes, which is a vast and still ongoing field of research. Finally, this research also sheds lights on soil water repellency at the molecular scale. I investigate structural properties of organic matter that are found in soil and find that zwitterionic lipid aggregates bind to the surface of the clay. In this relatively new field, such molecular simulations will have significant scientific impact.
- Chemistry