Surface Wetting Is a Key Determinant of α-Synuclein Condensate Maturation

Abstract

-Synuclein self-assembles into amyloid fibrils during neurodegeneration. The protein can also self-assemble via liquid-liquid phase separation to form biomolecular condensates. The link between these processes is evident, as -synuclein condensates can mature into amyloids. However, the mechanisms driving this maturation remain largely unknown, particularly when incorporating pathological post-translational modifications known to affect -synuclein self-assembly in the absence of LLPS, such as N-terminal truncation. Moreover, condensates are primarily studied as isolated entities; however, it is increasingly evident that they interact with various cellular components and surfaces. Here, we developed a microscopy-based quantitative real-time imaging protocol to investigate how N-terminal truncation influences -synuclein condensate formation, well surface wetting, and maturation. We found that increasing -synuclein truncation, which reduces N-terminal hydrophobicity, inhibits condensate sedimentation, enhances surface wettability, and accelerates maturation. Additionally, by increasing well surface hydrophobicity we decreased -synuclein condensate wettability, delaying their maturation. Thus, we propose that enhanced wettability, which increases the condensate surface-to-volume ratio, promotes -synuclein nucleation at the condensate-bulk solution interface, thereby accelerating maturation. Our results reveal distinct mechanistic roles for -synuclein N-terminal residues and indicate that condensate wetting on cellular surfaces, such as synaptic vesicles, may drive toxic aggregate formation during neurodegeneration.