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

The conformational space of the tetrapeptide Ac-Lys-Pro-Gly-Ile-NMA fr om the beta-bend present in the third loop of short-chain snake venom neurotoxins was investigated with the aid of energy calculations, resu lting in the identification of an ensemble of beta-turn conformations. These results were compared with the experimentally determined confor mations, as observed using NMR and CD spectroscopy. A random coil conf ormation of the peptide is indicated in polar hydrogen-bonding solvent s. In less polar solvents the peptide backbone assumed a more rigid co nformation, as reflected by the existence of at least a type II beta-t urn conformation. (C) Munksgaard 1993.