At low ionic strength, alpha-synuclein began forming assemblies at a concentration close to 1 micromolar. Their apparent mass settled near 300 to 400 kilodaltons, or kDa, equivalent to roughly 20 to 26 alpha-synuclein molecules, and did not increase as the protein concentration rose.
The peer-reviewed study also found a marked difference under higher-salt conditions. At 200 millimolar NaCl, alpha-synuclein was associated with much larger nanoclusters weighing about 1 to 5 megadaltons, or MDa. After five days at high salt, the low-salt assemblies had disappeared as condensates appeared, and some fibrils were visible after seven days.
A compact structure with a distinctive shape
The researchers asked whether alpha-synuclein forms a previously unknown assembly state in solution at low ionic strength and whether its properties support a micelle-like organization. Their protein panel included wild-type alpha-synuclein, a NAC variant, K-to-Q charge variants and an A140C variant.
They combined mass photometry, transmission electron microscopy, atomic force microscopy, dynamic light scattering and flow-induced dispersion analysis. The measurements examined apparent mass, particle shape, transport behavior and responses to changing chemical conditions.
Transmission electron microscopy showed narrow, spherical particles with similar dimensions across the tested protein concentrations. Median diameters were 26 ± 5 nanometres at 20 micromolar, 28 ± 6 nanometres at 50 micromolar and 29 ± 4 nanometres at 200 micromolar. The images showed occasional clustering, but no particle fusion was detected.
The assemblies were a very low-abundance species, and the study detected them differently with different techniques. As a separate check, flow-induced dispersion analysis detected a transient higher-order signal relative to the diffusive monomer peak when samples contained 25% PEG-8000. That supported the presence of larger species in solution, but did not by itself identify their molecular composition.
Why the researchers describe them as micelle-like
The assembly's apparent mass depended on where charges were altered in the protein. Variants in the amphipathic domain showed progressively lower apparent mass as lysines were removed. For the KQ12 variant, the apparent mass fell by roughly twofold, from about 200 kDa to about 100 kDa. Charge variants in the NAC region changed little, while an isolated Core variant showed no detectable nanoscale assemblies.
Finite size, a narrow particle distribution, the lack of detected fusion and sensitivity to charge location are consistent with a micelle-like organization. The charge-location result is mechanistic support for that model, not direct structural proof.
Comparison proteins behaved differently. TDP43-LCD nanoclusters ranged from 100 to 900 kDa and increased in apparent mass as protein concentration rose. Ddx4N1 nanoclusters stabilized at a maximum of 900 kDa. Under the NaCl condition, TDP43-LCD mass was unchanged, whereas Ddx4N1 mass decreased.
The state was fragile, but reversible
The assemblies were chemically labile. As urea concentration increased, the non-diffusive LSA signal progressively weakened, indicating lower stability than the alpha-synuclein fibrils or oligomers cited for comparison. The study did not report a precise concentration at which the particles dissolved.
During heating, static light scattering showed a broad transition to a fully monomeric state near 75°C. Cooling across that transition restored higher-order assemblies, indicating reversible disassembly and reformation under the tested conditions.
The salt difference also appeared in a fluorescent aging test. Over seven days, no increase in thioflavin T, or ThT, fluorescence was detected without NaCl, while the 200 mM NaCl condition showed a rapid increase. ThT is a surrogate reporter, and aggregate sedimentation could also affect the signal.
A result for the test tube, not yet for living systems
The findings came from purified recombinant proteins in defined in vitro buffers. The microscopy measurements used dried samples, which may alter native dimensions, and the study did not directly resolve the molecular structure of the assemblies. Their very low abundance also limited detection and structural characterization.
The experiments therefore describe a controlled solution state. They do not establish that the assemblies occur or function in cells, or that the salt-dependent transitions observed here take place in living systems.
The work reports support from ERC CoG 101088163 EMMA, the Lundbeck Foundation, Horizon MSCA, Dutch Sector Plan beta, Green DFF, the Novo Nordisk Foundation and a Lundbeck Experiment Grant. The authors state that funders had no role in the study or publication process, report no conflicts of interest and say the underlying data are openly available in a Zenodo repository.
Paper data and sources
Original title: α-Synuclein Forms Distinct Micelle-Like Assemblies at Low Ionic Strengths.
Authors: Sophie Hertel, Soumik Ray, Federica Saraceno et al.
Journal/Repository: Advanced science (Weinheim, Baden-Wurttemberg, Germany)
Status: Peer-reviewed
First online: 2026-08-21
DOI: 10.1002/advs.77300
Original paper