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

Fuscopeptins are phytotoxic amphiphilic lipodepsipeptides containing 19 ami no acid residues. They are produced by the plant pathogenic bacterium Pseud omonas 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 b iological properties have been reported previously. CD and NMR spectroscopy investigations in solution revealed the absence of identifiable elements o f secondary and tertiary structure for these molecules. Fuscopeptin B appea rs to be completely unstructured in aqueous solution, and has a large molec ular flexibility. A dramatic conformational change was observed upon additi on of trifluoroethanol. This study reports the complete interpretation of t he two-dimensional NMR spectra and the NOE results obtained for fuscopeptin B in water/trifluoroethanol solutions; the signals relative to the peptidi c moiety are identical to those observed for fuscopeptin A. The results of this investigation were used to determine the solution structure of fuscope ptin B by computer simulations applying distance geometry and simulated ann ealing procedures. In water/trifluoroethanol solutions the peptidic region appears to have a partly helical structure. The lactonic ring assumes defin ed conformations very similar to these already reported for other lipodepsi peptides. The structure for fuscopeptin B in solution is also valid for fus copeptin A because of the negligible structural difference between the two metabolites.