Micron-sized DNA–gelatin coacervates generated by ionic complexation in the presence of a nonionic polysaccharide

HYPOTHESIS: DNA-protein coacervate microparticles can be formed via ionic complexation between DNA and a protein, facilitated by the presence of a nonionic polymer. Despite recent advances in understanding membraneless organelles (MLOs) in eukaryotic cells, their formation through liquid-liquid phase separation remains incompletely elucidated. We hypothesized that due to their opposite charges, DNA and gelatin readily form micron-sized coacervates, and particle formation is facilitated by adding a polymer immiscible with gelatin. EXPERIMENTS: Formation of coacervate microparticles was essayed in the model system composed of an anionic protein (gelatin), a nonionic polysaccharide (dextran) and DNA from salmon testes. The gelatin-dextran system was chosen because these biopolymers exhibit a broad immiscibility region in their phase diagram, and can form water-in-water emulsions. Particle size was studied as a function of composition parameters, and molecular interactions were evaluated by rheology. FINDINGS: Microparticles mainly composed of gelatin and DNA were successfully synthesized, while dextran remained predominantly in the continuous phase. Particle formation was driven by electrostatic interactions between positively charged gelatin and negatively charged DNA, further facilitated by the immiscibility between gelatin and dextran. Rheological analyses confirmed that these spherical particles are indeed microgels, exhibiting high viscosity, pseudoplastic behavior and significant cohesive energy, driven by electrostatic gelatin-DNA interactions. Additionally, particle size could be finely tuned by adjusting the concentrations of the biopolymers.