Function and dysfunction of α-synuclein: probing conformational changes and aggregation by single molecule fluorescence

Abstract

The aggregation and deposition of the neuronal protein α-synuclein in the substantia nigra region of the brain is a key pathological feature of Parkinson's disease. α-Synuclein assembles from a monomeric state in solution, which lacks stable secondary and tertiary contacts, into highly structured fibrillar aggregates through a pathway which involves the population of multiple oligomeric species over a range of time scales. These features make α-synuclein well suited for study with single-molecule techniques, which are particularly useful for characterizing dynamic, heterogeneous samples. Here, we review the current literature featuring single-molecule fluorescence studies of α-synuclein and discuss how these studies have contributed to our understanding of both its function and its role in disease.

Figure 1

Schematic of AS. Shown in red is the N-terminal membrane binding region (residues 1–95), light gray is the central hydrophobic domain, and dark gray is the negatively charged C-terminal region. PD-associated disease mutations are marked in yellow.

Figure 2

The conformational states of AS. Cartoons in green show three of the most well studied conformational states of AS. The unfolded state (U) is largely disordered, though the hydrodynamic radius is not as large as expected for a fully random coil. The U-state transitions to an intermediate state (I) upon binding of SDS monomers or micelles. The I-state is also known as the hairpin or horseshoe conformational state. The folded state (F) can be populated via either the I-state, upon additional SDS monomer binding, or from the U-state upon binding to large unilamellar vesicles (LUV) or extended SDS structures. The SDS concentrations given are sub-CMC, where monomer SDS binds to AS. The F-state is also known as the extended helical conformation when bound to LUVs. The U, I, F nomenclature is from Reference .