Characterizations of critical processes in liquid-liquid phase separation of the elastomeric protein-water system:...

Biological self-assembly process of tropoelastin in an extracellular space, viewed as a key step of the elastogenesis, can be mimicked by the temperature-dependent coacervation of the elastin-related polypeptide-water system. Early and late stages of the phase separation behavior of the bovine neck ligamental alpha-elastin-water system were examined respectively by the laser light scattering photometry and phase contrast microscopy. Changes in the hydrodynamic size of molecular assemblies and visible microcoacervate droplet size were traced as a function of the concentration of alpha-elastin and temperature. Near the critical point, alpha-elastin concentration of 0.11 mg/mL and temperature of 21.5 degrees C, the phase separation was initiated after fast increase of the hydrodynamic size of primary aggregates as scattering particles and followed by the appearance of larger microcoacervate droplets with a broad size distribution. Whereas in the off-critical region, slow decrease of the hydrodynamic size of primary particles induced phase separation with smaller droplets of a narrow size distribution. Observation of the phase separation processes in the alpha-elastin-water system with metal chlorides and hydrophobic synthetic model polypeptide-water system indicated that the fast and slow molecular assembly processes were based on the fundamental hydrophobic interactions and involvements of electrostatic interactions between charged amino acid residues, respectively.