alpha-synuclein and 1-2-dioleoyl-sn-glycero-3-phosphoglycerol

Amyloid formation of the protein α-synuclein promotes neurodegeneration in Parkinson's disease. The normal function of α-synuclein includes synaptic vesicle transport and fusion, and the protein binds strongly to negatively charged vesicles in vitro. Here, we demonstrate that nonresonant angle-resolved second-harmonic scattering detects α-synuclein binding to liposomes through changes in water orientational correlations and can thus be used as a high-accuracy and high-throughput label-free probe of protein-liposome interactions. The obtained results support a binding model in which the N-terminus of α-synuclein adopts an α-helical conformation that lies flat on the vesicle surface while the negatively charged C-terminus remains in solution.

Topics: alpha-Synuclein; Escherichia coli; Liposomes; Membrane Proteins; Phosphatidylglycerols; Protein Binding; Protein Conformation, alpha-Helical; Water

Numerous pathological amyloid proteins spread from cell to cell during neurodegenerative disease, facilitating the propagation of cellular pathology and disease progression. Understanding the mechanism by which disease-associated amyloid protein assemblies enter target cells and induce cellular dysfunction is, therefore, key to understanding the progressive nature of such neurodegenerative diseases. In this study, we utilized an imaging-based assay to monitor the ability of disease-associated amyloid assemblies to rupture intracellular vesicles following endocytosis. We observe that the ability to induce vesicle rupture is a common feature of α-synuclein (α-syn) assemblies, as assemblies derived from WT or familial disease-associated mutant α-syn all exhibited the ability to induce vesicle rupture. Similarly, different conformational strains of WT α-syn assemblies, but not monomeric or oligomeric forms, efficiently induced vesicle rupture following endocytosis. The ability to induce vesicle rupture was not specific to α-syn, as amyloid assemblies of tau and huntingtin Exon1 with pathologic polyglutamine repeats also exhibited the ability to induce vesicle rupture. We also observe that vesicles ruptured by α-syn are positive for the autophagic marker LC3 and can accumulate and fuse into large, intracellular structures resembling Lewy bodies in vitro. Finally, we show that the same markers of vesicle rupture surround Lewy bodies in brain sections from PD patients. These data underscore the importance of this conserved endocytic vesicle rupture event as a damaging mechanism of cellular invasion by amyloid assemblies of multiple neurodegenerative disease-associated proteins, and suggest that proteinaceous inclusions such as Lewy bodies form as a consequence of continued fusion of autophagic vesicles in cells unable to degrade ruptured vesicles and their amyloid contents.

Topics: alpha-Synuclein; Amyloidogenic Proteins; Animals; Autophagy; Biological Transport; Brain; Cells, Cultured; Female; Fluoresceins; Humans; Lewy Bodies; Male; Neurons; Parkinson Disease; Phosphatidylglycerols; Rats; Transport Vesicles; Unilamellar Liposomes

Multivalent membrane binding sites on the α-synuclein oligomer result in clustering of vesicles and hemifusion of negatively charged model membranes. These multivalent, biological nanoparticles are reminiscent of inorganic nanoparticles in their interactions with membranes. Alpha-synuclein oligomers induce lipid exchange efficiently, with fewer than 10 oligomers/vesicle required to complete hemifusion. No full fusion or vesicle content mixing is observed.

Topics: alpha-Synuclein; Amyloid; Fluorescent Dyes; Nanoparticles; Phosphatidylglycerols; Protein Multimerization; Unilamellar Liposomes

Single-amino acid mutations in the human α-synuclein (αS) protein are related to early onset Parkinson's disease (PD). In addition to the well-known A30P, A53T, and E46K mutants, recently a number of new familial disease-related αS mutations have been discovered. How these mutations affect the putative physiological function of αS and the disease pathology is still unknown. Here we focus on the H50Q and G51D familial mutants and show that like wild-type αS, H50Q and G51D monomers bind to negatively charged membranes, form soluble partially folded oligomers with an aggregation number of ~30 monomers under specific conditions, and can aggregate into amyloid fibrils. We systematically studied the ability of these isolated oligomers to permeabilize membranes composed of anionic phospholipids (DOPG) and membranes mimicking the mitochondrial phospholipid composition (CL:POPE:POPC) using a calcein release assay. Small-angle X-ray scattering studies of isolated oligomers show that oligomers formed from wild-type αS and the A30P, E46K, H50Q, G51D, and A53T disease-related mutants are composed of a similar number of monomers. However, although the binding affinity of the monomeric protein and the aggregation number of the oligomers formed under our specific protocol are comparable for wild-type αS and H50Q and G51D αS, G51D oligomers cannot disrupt negatively charged and physiologically relevant model membranes. Replacement of the membrane-immersed glycine with a negatively charged aspartic acid at position 51 apparently abrogates membrane destabilization, whereas a mutation in the proximal but solvent-exposed part of the membrane-bound α-helix such as that found in the H50Q mutant has little effect on the bilayer disrupting properties of oligomers.

Topics: alpha-Synuclein; Cell Membrane Permeability; Fluoresceins; Humans; Membranes, Artificial; Multiprotein Complexes; Mutation, Missense; Parkinson Disease; Phosphatidylcholines; Phosphatidylethanolamines; Phosphatidylglycerols; Protein Binding; Scattering, Small Angle; X-Ray Diffraction

Previous studies indicate that binding of alpha-synuclein to membranes is critical for its physiological function and the development of Parkinson's disease (PD). Here, we have investigated the association of fluorescence-labeled alpha-synuclein variants with different types of giant unilamellar vesicles using confocal microscopy. We found that alpha-synuclein binds with high affinity to anionic phospholipids, when they are embedded in a liquid-disordered as opposed to a liquid-ordered environment. This indicates that not only electrostatic forces but also lipid packing and hydrophobic interactions are critical for the association of alpha-synuclein with membranes in vitro. When compared to wild-type alpha-synuclein, the disease-causing alpha-synuclein variant A30P bound less efficiently to anionic phospholipids, while the variant E46K showed enhanced binding. This suggests that the natural association of alpha-synuclein with membranes is altered in the inherited forms of Parkinson's disease.

Topics: alpha-Synuclein; Amino Acid Sequence; Anions; Binding Sites; Cell Membrane; Fatty Acids; Fluorescent Dyes; Hydrophobic and Hydrophilic Interactions; Lipids; Microscopy, Fluorescence; Molecular Sequence Data; Molecular Weight; Mutation; Parkinson Disease; Phosphatidic Acids; Phosphatidylcholines; Phosphatidylglycerols; Phosphatidylinositol 4,5-Diphosphate; Phosphatidylserines; Phospholipids; Protein Binding; Protein Conformation; Protein Structure, Secondary; Protein Structure, Tertiary; Rhodamines; Static Electricity; Surface Properties; Unilamellar Liposomes