SOLUTION CONFORMATION OF THE PSEUDOMONAS-SYRINGAE PV SYRINGAE PHYTOTOXIC LIPODEPSIPEPTIDE SYRINGOPEPTIN 25-A - 2-DIMENSIONAL NMR, DISTANCE GEOMETRY AND MOLECULAR-DYNAMICS

Syringopeptin 25-A is a phytotoxic amphiphilic lipodepsipeptide contai ning 25 amino acid residues, produced by some isolates of the plant pa thogenic bacterium Pseudomonas syringae pv. syringae. Previous papers have reported its covalent structure and some of its biological proper ties. Attention has now been directed to define its conformation in so lution, a structural feature regarded as important for understanding i ts possible role in the bacterial colonization of host plants, acid it s toxic action on the plant cell. Here we report the stereochemistry o f its amino acid components, the complete interpretation of the two-di mensional NMR spectra and NOE data, and finally the structure obtained by computer simulations applying distance geometry and molecular dyna mics procedures. The conformation of syringopeptin 25-A in aqueous sol ution includes three different structural regions interrupted by rigid 2,3-dehydro-2-aminobutyric acid residues: a loop from residue 2 to 6, a helicoidal zone from 8 to 15, and the lactone ring from 18 to 25. T he three-dimensional structure of the lactone moiety is very similar t o that of two previously studied bioactive lipodepsinonapeptides. Prel iminary circular dichroism evidence of conformational variations in so lution of trifluoroethanol, which simulates a membrane-like environmen t, are also reported.