Cooperativity of α-Synuclein Binding to Lipid Membranes.

Katarzyna Makasewicz,Sara Linse,Marco Fornasier,Björn Stenqvist,Alexandra Andersson,Stefan Wennmalm,Peter Jönsson,Emma Sparr

doi:10.1021/acschemneuro.1c00006

Abstract

Cooperative binding is a key feature of metabolic pathways, signaling, and transport processes. It provides tight regulation over a narrow concentration interval of a ligand, thus enabling switching to be triggered by small concentration variations. The data presented in this work reveal strong positive cooperativity of α-synuclein binding to phospholipid membranes. Fluorescence cross-correlation spectroscopy, confocal microscopy, and cryo-TEM results show that in excess of vesicles α-synuclein does not distribute randomly but binds only to a fraction of all available vesicles. Furthermore, α-synuclein binding to a supported lipid bilayer observed with total internal reflection fluorescence microscopy displays a much steeper dependence of bound protein on total protein concentration than expected for independent binding. The same phenomenon was observed in the case of α-synuclein binding to unilamellar vesicles of sizes in the nm and μm range as well as to flat supported lipid bilayers, ruling out that nonuniform binding of the protein is governed by differences in membrane curvature. Positive cooperativity of α-synuclein binding to lipid membranes means that the affinity of the protein to a membrane is higher where there is already protein bound compared to a bare membrane. The phenomenon described in this work may have implications for α-synuclein function in synaptic transmission and other membrane remodeling events.

Highlights

Allostery was discovered in 1961 by Jaques Monod, who referred to the phenomenon as the second secret of life.[1]
We study the distribution of α-synuclein over the membrane surface area in both regimes, focusing on the conditions of membrane excess, using confocal microscopy, total internal reflection fluorescence (TIRF) microscopy, fluorescence cross-correlation spectroscopy (FCCS), and cryogenic transmission electron microscopy
When fluorescently labeled α-synuclein is added to lipid membranes in the form of giant unilamellar vesicles (GUVs), the protein distributes in a nonrandom way, as observed with a confocal microscope (Figure 1)

Summary

Introduction

Allostery was discovered in 1961 by Jaques Monod, who referred to the phenomenon as the second secret of life.[1]. Constant brightness per particle and total red fluorescence signal from vesicles in the L/ P range 800−2000 imply no redistribution of α-synuclein-647 molecules on excess vesicles available for binding.

Results

Conclusion