Multiple interconverting conformers of the cyclic tetrapeptide tentoxin, [cyclo-(L-MeAla1-L-Leu2-MePhe[(Z) delta]3-Gly4)], as seen by two-dimensional 1H-nmr spectroscopy.

The conformations of the phytotoxic cyclic tetrapeptide tentoxin [cyclo-(L-MeAla1-L-Leu2-MePhe[(Z) delta]3-Gly4)] have been studied in aqueous solution by two-dimensional proton nmr at various temperatures. Contrary to what is observed in chloroform, tentoxin exhibits multiple exchanging conformations in water. Aggregation phenomena were also observed. Four conformations with different proportions (51, 37, 8, and 4%) were observed at -5 degrees C. Models were constructed from nmr parameters and restrained molecular dynamics simulations. All the models exhibit cis-trans-cis-trans conformation of the amide bond sequence. The conversion from one form to another is accomplished by a conformational peptide flip consisting of a 180 degree rotation of a nonmethylated peptide bond.