Reversible modulation of protocell volume via collective response of functional protein in its membrane

Volume change plays an important role in biological cells to regulate their internal microenvironment. To adapt to the rapid variation of the surface area during the volume change, the lipid membrane is dynamically modulated via membrane folding invagination, or spontaneous uptake or release of lipid molecules under osmotic pressure. Here, we demonstrate an alternative approach to design a functional protocellular system capable of dynamically adjusting its volume and intracellular microenvironment in response to the alteration of pH. By assembling and subsequently cross-linking pH-responsive caseinate at the water-oil interface, the caseinate-based protocell with more than ten thousand caseinate units in its membrane was established and showed a reversible volume and pore size change to pH variation due to the collective response of the caseinate in the membrane, which could be used to control the spatial distribution of proto-organelle by regulating of the viscosity inside the protocell.