Four peptides, C1 (spanning the helical segment of human neuropeptide Y from residue 15 to residue 29), C2 (spanning the helical segment of 21 to 31), C3 (the C-terminal fragment of neuropeptide Y involving residues 20 to 36) and P34-C3 (replacement of the glutamine with proline in position 34 of C3) were synthesized to study interaction between species. The information about the intermolecular interactions was extracted from their self-assembly behaviors. The results from CD and NMR showed that the addition of 2, 2, 2-trifluoroethanol (TFE) induces a stable amphipathic helix in each peptides and an extended helix was formed at the N-terminal of C1 and the C-terminal of C3. Pulsed field gradient NMR data revealed that C3 may undergo an enhanced interaction with TFE and a more favorable self-assembly as temperature was increased. In contrast, other three peptides were found to form larger size of oligomers at lower temperature and continuously dissociate into the monomeric form with increased temperature. Our results demonstrate that the self-assembly behavior may be tuned by the entropy and the energetics contributed by an extended helical conformation at terminus.
