Driving Force for the Complexation of Charged Polypeptides

• Published in: The journal of physical chemistry. B Vol. 124; no. 7; pp. 1285 - 1292
• Main Authors: Singh, Aditya N, Yethiraj, Arun
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 20.02.2020
• Subjects: Molecular Dynamics Simulation; Peptides - chemistry; Physical Phenomena; Polyelectrolytes - chemistry; Thermodynamics
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/acs.jpcb.9b09553

The phase separation of oppositely charged polyelectrolytes in solution is of current interest. In this work, we study the driving force for polyelectrolyte complexation using molecular dynamics simulations. We calculate the potential of mean force between poly­(lysine) and poly­(glutamate) oligomers using three different force fields, an atomistic force field and two coarse-grained force fields. There is qualitative agreement between all force fields, i.e., the sign and magnitude of the free energy and the nature of the driving force are similar, which suggests that the molecular nature of water does not play a significant role. For fully charged peptides, we find that the driving force for association is entropic in all cases when small ions either neutralize the poly ions, or are in excess. The removal of all counterions switches the driving force, making complexation energetic. This suggests that the entropy of complexation is dominated by the counterions. When only 6 residues of a 11-mer are charged, however, the driving force is energetic in the abscence of excess salt. The simulations shed insight into the mechanism of complex coacervation and the importance of realistic models for the polyions.