Conformations in solution of the fuscopeptins. Phytotoxic metabolites of Pseudomonas fuscovaginae

Fuscopeptins are phytotoxic amphiphilic lipodepsipeptides containing 19 amino acid residues. They are produced by the plant pathogenic bacterium Pseudomonas fuscovaginae in two forms, A and B, which differ only in the number of methylene groups in the fatty acid chain. Their covalent structure and biological properties have been reported previously. CD and NMR spectroscopy investigations in solution revealed the absence of identifiable elements of secondary and tertiary structure for these molecules. Fuscopeptin B appears to be completely unstructured in aqueous solution, and has a large molecular flexibility. A dramatic conformational change was observed upon addition of trifluoroethanol. This study reports the complete interpretation of the two-dimensional NMR spectra and the NOE results obtained for fuscopeptin B in water/trifluoroethanol solutions; the signals relative to the peptidic moiety are identical to those observed for fuscopeptin A. The results of this investigation were used to determine the solution structure of fuscopeptin B by computer simulations applying distance geometry and simulated annealing procedures. In water/trifluoroethanol solutions the peptidic region appears to have a partly helical structure. The lactonic ring assumes defined conformations very similar to those already reported for other lipodepsipeptides. The structure for fuscopeptin B in solution is also valid for fuscopeptin A because of the negligible structural difference between the two metabolites.