EXPERIMENTAL STUDIES AND POTENTIAL-ENERGY CALCULATIONS OF THE BLOCKEDTETRAPEPTIDE AC-LYS-GLN-GLY-ILE-NMA FROM THE 3RD LOOP OF A SHORT-CHAIN SNAKE-VENOM NEUROTOXIN

The conformational space of the tetrapeptide Ac-Lys-Gln-Gly-IIe-NMA fr om the beta-bend in the third loop of a short-chain snake venom neurot oxin was investigated with the aid of energy calculations. It was show n that this peptide has a preference for an alpha-helical conformation . This result was compared with the experimentally determined conforma tions, as observed using NMR and CD spectroscopy. With NMR spectroscop y 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-heli cal conformations is present in TFE. These results indicate that addit ional long-range interactions also pray a role in the conformation of this tetrapeptide in the protein. (C) Munksgaard 1994.