Biomolecular condensates are central to cellular organization, yet how they interact with membranes remains poorly understood. To address this, we use cell-mimetic systems in which Giant Unilamellar Vesicles (GUVs) with defined lipid compositions provide controlled compartments for condensate assembly. By spatiotemporally regulating nucleotide-peptide condensate formation inside GUVs, we mimic cellular environments where condensates dynamically assemble. We specifically investigate the role of electrostatics in controlling condensate-membrane interactions and their impact on condensate size. Screening experiments with varying salt concentrations confirm that these interactions are charge-dependent: altering the surface charge of condensates or membranes modulates both the strength and outcome of their association. Weak electrostatic interactions allow membrane budding around condensates, whereas strong interactions generate a wrinkled membrane phenotype that constrains condensate growth. Fluorescence recovery after photobleaching (FRAP) shows that condensate coupling during wrinkling significantly reduces membrane diffusion. High-resolution imaging, including TEM, further reveals condensates embedding into folded membrane structures. Together, these results indicate that membranes restrict condensate size through electrostatically mediated remodeling, yielding dimensions comparable to those observed in vivo. Our study uncovers electrostatic forces as central regulators of condensate size at membranes and highlights the power of cell-mimetic models in dissecting the physical principles underlying cellular organization.
Karthika S. Nair (Sun,) studied this question.