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Effects of an Extended Amphipathic Helix on Intermolecular Interactions and Self-Assembly of Peptides via Pulsed Field Gradient Nuclear Magnetic Resonance

Intermolecular interactions are of fundamental importance to fully comprehend the formation mechanism of a nanostructure created by peptides. Four peptides, segmented from human neuropeptide Y (hNPY), were synthesized in this work to study the interaction between species. Information about intermolecular interactions was extracted from their self-assembly behaviors. The results from pulsed field gradient NMR data revealed that one of the peptides may undergo a more favorable self-assembly as temperature was increased, while other three peptides were found to form larger self-assemblies at lower temperatures and continuously dissociate into the monomeric form with increasing temperature. We characterized the changes of the oligomeric states with respect to temperature to infer the effects of entropy and interacting energetics on the self-assembly behavior. We demonstrated that an extended C-terminal helix may improve the binding of TFE, and as a result, entropy is gained via the transfer of the TFE cluster from the interface between monomeric peptides into the bulk solvent. This observation suggests that the self-assembly behavior may be modulated by the entropy and the energetics contributed by the helical segments in a self-assembly process.