Experimental studies and potential-energy calculations of the blocked tetrapeptide Ac-Lys-Gln-Gly-Ile-NMA from the third loop of a short-chain snake venom neurotoxin.

The conformational space of the tetrapeptide Ac-Lys-Gln-Gly-Ile-NMA from the beta-bend in the third loop of a short-chain snake venom neurotoxin was investigated with the aid of energy calculations. It was shown that this peptide has a preference for an alpha-helical conformation. This result was compared with the experimentally determined conformations, as observed using NMR and CD spectroscopy. With NMR spectroscopy a random-coil conformation of the peptide is indicated in H2O, DMSO and TFE. The results from the CD experiments suggest that the peptide exists as a random coil in water, but a small population of alpha-helical conformations is present in TFE. These results indicate that additional long-range interactions also play a role in the conformation of this tetrapeptide in the protein.