MULTIPLE INTERCONVERTING CONFORMERS OF THE CYCLIC TETRAPEPTIDE TENTOXIN, -(L-MEALA(1)-L-LEU(2)-MEPHE[(Z)DELTA](3)-GLY(4))], AS SEEN BY 2-DIMENSIONAL H-1-NMR SPECTROSCOPY

The conformations of the phytotoxic cyclic tetrapeptide tentoxin o-(L- MeAla(1)-L-Leu(2)-MePhe[(Z)Delta](3)-Gly(4))] have been studied in aqu eous solution by two-dimensional proton nmr at various temperatures. C ontrary to what is observed in chloroform, tentoxin exhibits multiple exchanging conformations in water. Aggregation phenomena were also obs erved. Four conformations with different proportions (51, 37, 8, and 4 %) were observed at -5 degrees C. Models were constructed from nmr par ameters and restrained molecular dynamics simulations. All the models exhibit cis-trans-cis-trans conformation of the amide bond sequence. T he conversion from one form to another is accomplished by a conformati onal peptide flip consisting of a 180 degrees rotation of a nonmethyla ted peptide bond. (C) 1995 John Wiley & Sons, Inc.