Phase transitions are important to understand cell dynamics, and the maturation of liquid droplets is relevant to neurodegenerative disorders. We combined NMR and Raman spectroscopies with microscopy to follow, over a period of days to months, droplet maturation of the protein fused in sarcoma (FUS). Our study reveals that the surface of the droplets plays a critical role in this process, while RNA binding prevents it. The maturation kinetics are faster in an agarose-stabilized biphasic sample compared with a monophasic condensed sample, owing to the larger surface-to-volume ratio. In addition, Raman spectroscopy reports structural differences upon maturation between the inside and the surface of droplets, which is comprised of β-sheet content, as revealed by solid-state NMR. In agreement with these observations, a solid crust-like shell is observed at the surface using microaspiration. Ultimately, matured droplets were converted into fibrils involving the prion-like domain as well as the first RGG motif.

相变对于理解细胞动力学很重要，液滴的成熟与神经退行性疾病相关。我们将核磁共振、拉曼光谱与显微镜相结合，在几天到几个月的时间内跟踪肉瘤融合蛋白 (FUS) 的液滴成熟情况。我们的研究表明，液滴表面在此过程中发挥着关键作用，而 RNA 结合则阻止了这一过程。与单相浓缩样品相比，琼脂糖稳定的双相样品的成熟动力学更快，因为其表面积与体积之比更大。此外，拉曼光谱报告了液滴内部和表面成熟时的结构差异，这些差异由固态 NMR 揭示的 β-折叠内容组成。与这些观察结果一致，使用微抽吸在表面观察到坚固的壳状壳。最终，成熟的液滴转化为包含朊病毒样结构域以及第一个 RGG 基序的原纤维。