Enzymatic degradation of liquid droplets of DNA is modulated near the phase boundary

Biomolecules can undergo liquid-liquid phase separation (LLPS), forming dense droplets that are increasingly understood to be important for cellular function. Analogous systems are studied as early-life compartmentalization mechanisms, for applications as protocells, or as drug-delivery vehicles. In many of these situations, interactions between the droplet and enzymatic solutes are important to achieve certain functions. To explore this, we carried out experiments in which a model LLPS system, formed from DNA `nanostar' particles, interacted with a DNA-cleaving restriction enzyme, Sma~I, whose activity degraded the droplets, causing them to shrink with time. By controlling adhesion of the DNA droplet to a glass surface, we were able to carry out time-resolved imaging of this `active dissolution' process. We found that the scaling properties of droplet shrinking were sensitive to the proximity to the dissolution  (`boiling') temperature of the dense liquid: for systems far from the boiling point, enzymes acted only on the droplet surface, while systems poised near the boiling point permitted enzyme penetration. This was corroborated by the observation of enzyme-induced vacuole-formation (`bubbling') events, which can only occur through enzyme internalization, and which occurred only in systems poised near the boiling point. Overall, our results demonstrate a mechanism through which the phase stability of a liquid affects its enzymatic degradation through modulation of enzyme transport properties.

Methods
Dataset collection is described fully in the associated paper.

生物分子可发生液-液相分离（liquid-liquid phase separation, LLPS），形成致密液滴，如今学界愈发认识到这类液滴对细胞功能具有关键意义。类似体系被作为早期生命区室化机制、原细胞（protocells）应用载体或药物递送载体开展研究。在诸多此类场景中，液滴与酶类溶质间的相互作用对于实现特定功能至关重要。

为此我们开展了相关实验：以DNA纳米星（DNA nanostar）颗粒构建的模型LLPS体系，与可切割DNA的限制性内切酶SmaI发生相互作用；该酶的活性会降解液滴，使其随时间逐渐收缩。通过调控DNA液滴与玻璃表面的黏附作用，我们得以对这一"活性溶解"过程进行时间分辨成像。

我们发现，液滴收缩的标度特性与致密液体的溶解（"沸腾"）温度的接近程度密切相关：当体系远离该沸点时，酶仅作用于液滴表面；而当体系接近该沸点时，酶可渗透进入液滴内部。这一结论得到了酶诱导液泡形成（"冒泡"）现象的观测结果佐证：这类现象仅能通过酶的内化作用产生，且仅在接近沸点的体系中被观测到。

综上，本研究揭示了一种机制：液体的相稳定性可通过调控酶的转运特性，进而影响其酶促降解过程。

方法
数据集的完整采集流程详见相关研究论文。