The Dual Dependency of Varying Liposomes and Protein on Available αS Conformers

Abstract

α-Synuclein (αS) is a protein commonly found in protein aggregates associated with Parkinson’s disease (PD). This intrinsically disordered protein is known to regulate synaptic vesicle (SV) trafficking in the pre-synaptic clefts of most neurons. Improper trafficking of SVs results in miscommunication between neurons, which could lead to symptoms of PD such as muscular tremors. Despite the prevalence of PD, much is still left unknown about the mechanism that causes protein aggregation due to αS binding to SVs. SVs are unique membranes as a result of their high cholesterol content (45%) and small diameter (0.03 microns). Both factors induce strain in the membrane leading to high fusion potential of the SV. For this research two SV mimics (simple and complex) were designed, utilizing a mass spectrometry study on SV membrane composition.1 The simple SV mimic measured the effects of interacting head groups and cholesterol on membrane annealing in the presence of αS using a Carboxyfluorescein (CF) release assay .To further probe the question of conformational changes of αS in the presence of membrane Circular Dichroism (CD) monitored the secondary structure character. Both membrane annealing and a change in secondary structure were observed making it necessary to further investigate the relationship between protein and membrane with other methods. Using Differential Scanning Calorimetry (DSC) to monitor a lipid transition I hypothesized that αS has specificity for high curvature and complex composition of membrane. We tested this by varying liposome sizes and cholesterol content. Oppositely, the membranes impact on αS conformers was studied utilizing a DSC protein transition to see its effects. A conformational shift was found in the presence of complex SV mimic, showing αS’s conformational specificity for this highly complex mimic. Due to this preference, a binding mechanism using the complex SV mimic needs to be studied. The mechanism of αS binding to membrane has the potential to shed light on the pathogenesis of αS in amyloid formation. Through Isothermal Titration Calorimetry (ITC) we will predict a simulated binding model for αS that will give more information about possible reasons for protein aggregation and benefit future studies on PD.