Thrombin reshapes α-synuclein biochemical properties by N-terminal truncation

Abstract Proteolytic processing of α-Synuclein (Syn) contributes to the molecular diversity and toxicity of its aggregates in Parkinson’s disease, yet the proteases responsible for disease-relevant truncations remain incompletely defined. Here, we show that thrombin, a serine protease associated with inflammatory conditions, selectively cleaves Syn at Lys6–Gly7, generating a 7–140 fragment despite the presence of multiple potential cleavage sites. Cleavage is modulated by ionic strength and the conformational ensemble of Syn, with more extended states being preferentially cleaved. The resulting 7–140 fragment adopts a more compact conformational ensemble, delays the formation of aggregation-prone species, produces fibrils with altered morphology and shows reduced membrane-induced α-helix formation. Although 7–140 aggregates are modestly less toxic, the truncation also impairs physiological functions of the protein. These findings describe a mechanism by which an inflammation-associated protease, thrombin, may contribute to Parkinson’s disease by selectively modifying Syn structure, aggregation and function.