Coacervate Formation of Elastin-like Polypeptides in Explicit Aqueous Solution Using Coarse-Grained Molecular Dynamics Simulations

We performed coarse-grained molecular dynamics simulations with the Martini3 force field to investigate elastin-like polypeptide (ELP) coacervate formation and its internal structural and dynamics properties. Coacervate formation was found to be enhanced with increasing polymer concentration and polymer length, whereas no significant changes in the structural and dynamic properties inside the coacervate phase were observed among coacervates with different polymer concentrations and polymer lengths. The ion and water concentrations as well as the diffusion coefficients of water inside a coacervate were found to be reduced compared with that in bulk water. In addition, ELP phase separation behaviors were also observed experimentally and the trend of ELP concentration/length-dependent formation of a coacervate in the simulations was found to be in qualitative agreement with our experimental observations. Furthermore, simulations of the partitioning of RNA polymers demonstrate that an RNA polymer with ethyl (hydrophobic) modification favors the inside of a coacervate and shows a larger radius of gyration in comparison with a normal RNA polymer without modification (negatively charged). Our simulations provide a means to explore the requirement for control over coacervate formation and stability in a wide range of conditions. Understanding how specific sequence and structural features affect coacervate morphology and stability could help in the design of new biopolymers with additional desirable properties. [GRAPHICS]

Automated summary

We investigated the formation, internal structural and dynamics properties of elastin-like polypeptide (ELP) coacervates using coarse-grained molecular dynamics simulations. Coacervate formation was enhanced with higher polymer concentration and length. The structural and dynamic properties inside the coacervate phase remained unchanged for coacervates of different polymer concentrations and lengths. The ion and water concentrations as well as the diffusion coefficients of water inside a coacervate were reduced compared with bulk water. Experimental observations of ELP phase separation behaviors were qualitatively consistent with the simulation results. Additionally, our simulations showed that hydrophobic modification of an RNA polymer favored its localization inside a coacervate and led to a larger radius of gyration.