Copper (II) Interactions with Phosphatidylserine in Membranes: Biophysical Insights, Binding Mechanisms, and Physiological Consequences
Restricted (Penn State Only)
- Author:
- Reynolds, Christopher
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 13, 2023
- Committee Members:
- Paul Cremer, Chair & Dissertation Advisor
William Hancock, Outside Unit & Field Member
Alexey Silakov, Major Field Member
Lauren Zarzar, Major Field Member
Philip Bevilacqua, Program Head/Chair - Keywords:
- biophysical chemistry
transition metal ions
membranes
copper (II)
oxidative damage
supported lipid bilayer
microfluidic systems
binding
phosphatidylserine
lipids
stepwise
constants
stoichiometry
densities
concentrations
Gouy-Chapman theory
ionic strength
surface charge density
chelation
complexes
buffer molecules
physiological implications
HeLa cells
plasma membrane
necrotic cell death
hydrogen peroxide
harmful effects
mechanistic explanation
future experiments.
hrmful effects
Phospholipid membranes
oxidation
copper
membrane oxidation
membrane binding model
bivalent binding
Debye-Hukel Theory
Electrostatic screening
electric double layer
Necrotic cell death
copper induced cell death
Alzheimer's disease
Neurodegeneration
microfluidic devices
high-throughput microfluidics - Abstract:
- This dissertation investigates the biophysical chemistry of transition metal ion interactions with membranes, focusing on the essential nutrient copper (II). When misregulated, transition metal ions can cause significant oxidative damage. However, biophysical studies examining these interactions with membranes are scarce. This research employed a supported lipid bilayer model to explore the binding of transition metal ions to membranes. High-throughput microfluidic systems were frequently utilized in these experiments, and several design improvements were implemented. Using these devices, the stepwise binding constant of copper (II) to phosphatidylserine (PS) lipids was measured. Binding models were then developed, incorporating the measured stepwise binding constants, to predict the overall binding constant and stoichiometry of copper (II) binding to phosphatidylserine at different phosphatidylserine densities and copper concentrations. Subsequently, Gouy-Chapman theory predictions were tested on the copper (II)-PS system. The theory suggests that the binding affinity of copper (II) should be significantly influenced by changes in ionic strength and surface charge density. However, no such alteration was observed. This led to the conclusion that the chelation of copper (II) results in complex behavior, rendering the Gouy-Chapman theory inapplicable. One likely reason is the change in the net charge of copper (II) complexes upon chelation with buffer molecules. The physiological implications of the interaction between copper (II) and HeLa cell membranes were examined. The results showed that when HeLa cells were incubated with a combination of hydrogen peroxide and copper (II), the plasma membrane was damaged, leading to harmful necrotic cell death. This effect was copper (II)-specific and occurred at concentrations as low as 25-50 µM. Lastly, a comprehensive mechanistic explanation of copper (II) interactions with PS is provided, and potential future experiments are proposed.