α-Synuclein Oligomers Displace Monomeric α-Synuclein from Lipid Membranes.

Parkinson's disease (PD) is an increasingly prevalent and currently incurable neurodegenerative disorder linked to the accumulation of α-synuclein (αS) protein aggregates in the nervous system. While αS binding to membranes in its monomeric state is correlated to its physiological role, αS oligomerization and subsequent aberrant interactions with lipid bilayers have emerged as key steps in PD-associated neurotoxicity. However, little is known of the mechanisms that govern the interactions of oligomeric αS (OαS) with lipid membranes and the factors that modulate such interactions. This is in large part due to experimental challenges underlying studies of OαS-membrane interactions due to their dynamic and transient nature. Here, we address this challenge by using a suite of microfluidics-based assays that enable in-solution quantification of OαS-membrane interactions. We find that OαS bind more strongly to highly curved, rather than flat, lipid membranes. By comparing the membrane-binding properties of OαS and monomeric αS (MαS), we further demonstrate that OαS bind to membranes with up to 150-fold higher affinity than their monomeric counterparts. Moreover, OαS compete with and displace bound MαS from the membrane surface, suggesting that disruption to the functional binding of MαS to membranes may provide an additional toxicity mechanism in PD. These findings present a binding mechanism of oligomers to model membranes, which can potentially be targeted to inhibit the progression of PD.

Mechanism of biosurfactant adsorption to oil/water interfaces from millisecond scale tensiometry measurements.

Many biological molecules are by their nature amphiphilic and have the ability to act as surfactants, stabilizing interfaces between aqueous and immiscible oil phases. In this paper, we explore the adsorption kinetics of surfactin, a naturally occurring cyclic lipopeptide, at hexadecane/water interfaces and compare and contrast its adsorption behaviour with that of synthetic alkyl benzene sulfonate isomers, through direct measurements of changes in interfacial tension upon surfactant adsorption. We access millisecond time resolution in kinetic measurements by making use of droplet microfluidics to probe the interfacial tension of hexadecane droplets dispersed in a continuous water phase through monitoring their deformation when the droplets are exposed to shear flows in a microfluidic channel with regular corrugations. Our results reveal that surfactin rapidly adsorbs to the interface, thus the interfacial tension equilibrates within 300 ms, while the synthetic surfactants used undergo adsorption processes at an approximately one order of magnitude longer timescale. The approach presented may provide opportunities for understanding and modulating the adsorption mechanism of amphiphiles on a variety of interfaces in the context of life sciences and industrial applications.

Automated Ex Situ Assays of Amyloid Formation on a Microfluidic Platform.

Increasingly prevalent neurodegenerative diseases are associated with the formation of nanoscale amyloid aggregates from normally soluble peptides and proteins. A widely used strategy for following the aggregation process and defining its kinetics involves the use of extrinsic dyes that undergo a spectral shift when bound to ß-sheet-rich aggregates. An attractive route to carry out such studies is to perform ex situ assays, where the dye molecules are not present in the reaction mixture, but instead are only introduced into aliquots taken from the reaction at regular time intervals to avoid the possibility that the dye molecules interfere with the aggregation process. However, such ex situ measurements are time-consuming to perform, require large sample volumes, and do not provide for real-time observation of aggregation phenomena. To overcome these limitations, here we have designed and fabricated microfluidic devices that offer continuous and automated real-time ex situ tracking of the protein aggregation process. This device allows us to improve the time resolution of ex situ aggregation assays relative to conventional assays by more than one order of magnitude. The availability of an automated system for tracking the progress of protein aggregation reactions without the presence of marker molecules in the reaction mixtures opens up the possibility of routine noninvasive study of protein aggregation phenomena.