Aggregation dynamics of charged peptides in water: Effect of salt concentration.

Extensive molecular dynamics simulations have been employed to probe the effects of salts on the kinetics and dynamics of early-stage aggregated structures of steric zipper peptides in water. The simulations reveal that the chemical identity and valency of cation in the salt play a crucial role in aggregate dynamics and morphology of the peptides. Sodium ions induce the most aggregated structures, but this is not replicated equivalently by potassium ions which are also monovalent. Divalent magnesium ions induce aggregation but to a lesser extent than that of sodium, and their interactions with the charged peptides are also significantly different. The aggregate morphology in the presence of monovalent sodium ions is a compact structure with interpenetrating peptides, which differs from the more loosely connected peptides in the presence of either potassium or magnesium ions. The different ways in which the cations effectively renormalize the charges of peptides are suggested to be the cause of the differential effects of different salts studied here. These simulations underscore the importance of understanding both the valency and nature of salts in biologically relevant aggregated structures.