Biomolecular condensates concentrate macromolecules into discrete cellular foci without an encapsulating membrane. Condensates are often presumed to increase enzymatic reaction rates through increased concentrations of enzymes and substrates (mass action), although this idea has not been widely tested and other mechanisms of modulation are possible. Here we describe a synthetic system where the SUMOylation enzyme cascade is recruited into engineered condensates generated by liquid–liquid phase separation of multidomain scaffolding proteins. SUMOylation rates can be increased up to 36-fold in these droplets compared to the surrounding bulk, depending on substrate K_M. This dependency produces substantial specificity among different substrates. Analyses of reactions above and below the phase-separation threshold lead to a quantitative model in which reactions in condensates are accelerated by mass action and changes in substrate K_M, probaby due to scaffold-induced molecular organization. Thus, condensates can modulate reaction rates both by concentrating molecules and physically organizing them.

生物分子凝聚物将大分子浓缩到离散的细胞灶中，无需封装膜。通常认为冷凝物可以通过增加酶和底物的浓度（质量作用）来提高酶促反应速率，尽管这一想法尚未得到广泛测试，并且其他调节机制也是可能的。在这里，我们描述了一个合成系统，其中 SUMO 化酶级联被招募到通过多结构域支架蛋白的液-液相分离产生的工程缩合物中。与周围的体积相比，这些液滴中的 SUMO 化率最多可提高 36 倍，具体取决于底物K _M。这种依赖性在不同底物之间产生了显着的特异性。对高于和低于相分离阈值的反应的分析得出了一个定量模型，其中凝结物中的反应通过质量作用和底物K _M的变化而加速，这可能是由于支架诱导的分子组织所致。因此，缩合物可以通过浓缩分子和物理组织分子来调节反应速率。