Modi Nisha, Chen Siwei, Adjei Imelda N A, Franco Briana L, Bishop Kyle J M, Obermeyer Allie C
Department of Chemical Engineering, Columbia University New York USA
Department of Biomedical Engineering, Columbia University New York USA.
Chem Sci. 2023 Apr 19;14(18):4735-4744. doi: 10.1039/d2sc03838b. eCollection 2023 May 10.
Membraneless organelles within the living cell use phase separation of biomolecules coupled with enzymatic reactions to regulate cellular processes. The diverse functions of these biomolecular condensates motivate the pursuit of simpler models that exhibit primitive forms of self-regulation based on internal feedback mechanisms. Here, we investigate one such model based on complex coacervation of the enzyme catalase with an oppositely charge polyelectrolyte DEAE-dextran to form pH-responsive catalytic droplets. Upon addition of hydrogen peroxide "fuel", enzyme activity localized within the droplets causes a rapid increase in the pH. Under appropriate conditions, this reaction-induced pH change triggers coacervate dissolution owing to its pH-responsive phase behavior. Notably, this destabilizing effect of the enzymatic reaction on phase separation depends on droplet size owing to the diffusive delivery and removal of reaction components. Reaction-diffusion models informed by the experimental data show that larger drops support larger changes in the local pH thereby enhancing their dissolution relative to smaller droplets. Together, these results provide a basis for achieving droplet size control based on negative feedback between pH-dependent phase separation and pH-changing enzymatic reactions.
活细胞内的无膜细胞器利用生物分子的相分离以及酶促反应来调节细胞过程。这些生物分子凝聚物的多样功能促使人们寻求更简单的模型，这些模型基于内部反馈机制展现出原始的自我调节形式。在此，我们研究了这样一种模型，该模型基于过氧化氢酶与带相反电荷的聚电解质二乙氨基乙基葡聚糖的复合凝聚作用，形成对pH响应的催化液滴。加入过氧化氢“燃料”后，液滴内局部化的酶活性会导致pH迅速升高。在适当条件下，这种反应诱导的pH变化会因其pH响应相行为而触发凝聚物溶解。值得注意的是，酶促反应对相分离的这种去稳定作用取决于液滴大小，这是由于反应组分的扩散传递和去除。由实验数据得出的反应扩散模型表明，较大的液滴能支持局部pH的更大变化，从而相对于较小的液滴增强其溶解。总之，这些结果为基于pH依赖相分离和pH变化酶促反应之间的负反馈实现液滴大小控制提供了基础。
