Alpha-synuclein amyloid aggregation: From basic to translational research

Neurodegenerative diseases are a heterogeneous group of disorders affecting the lives of millions of people worldwide. A shared pathologic hallmark is the appearance of insoluble aggregates in the brain. The components of these are different, given a wide spectrum of neurodegenerative diseases. The presence of amyloid fibrils of specific proteins in the deposits allowed the identification of proteins involved in the development of the disease, and their study in vitro. Parkinson’s disease is considered a neurological disorder where spherical intraneuronal inclusions known as Lewy bodies are found in brain regions. The determination of inherited mutations has aided the research of alpha-synuclein, as one protein involved in the misfolding and deposition into Lewy bodies. Alpha-synuclein is an intrinsically disordered protein, found free or bound to membranes under physiological conditions. However, in pathological conditions adopt b-sheet conformations, resulting in amyloid fibrils. Many factors are modulating the pathways mentioned before, such as some regions of the protein, point mutations, and post-translational modifications. The physiological conditions could be addressed following the interaction of monomers with membranes, as one model for gaining knowledge in parameters such as membrane affinity, membrane-bound conformations, and even residues involved in the binding. Amyloid fibrils of alpha-synuclein can be generated in vitro, and be able to uncover fibril core, specific residues implicated in the aggregation process, stability and structure of fibrils. These tools permit the study of how different factors affect the physiological and pathological condition. Our study aimed to unravel the aggregation properties of alpha-synuclein through the characterization of conformational assemblies, as well as in terms of binding properties. Key factors in this process have been studied. A combination of kinetics assays, nuclear magnetic resonance, circular dichroism, dynamic light scattering, cell culture, fluorescent probes, electron and atomic force microscopy, was chosen to gain insight into all the features investigated. Structural changes induced for point mutations or post-translational modifications gave relevance to the implication of residue-specific in the pathological and functional state of the protein. We observed how particular amino acids can impair the in vitro amyloid assembly and even impact the binding to membranes. These factors are likely modulating structural conformations, that may be attributed then to the variety of alpha-synucleinopathies. The work presented here is a step forward towards understanding the role of alpha-synuclein in the pathology of Parkinson’s disease.