Cationic lipodepsipeptides from Pseudomonas spp. have been characterized for their structural and antimicrobial properties. In the present study, the structure of a novel lipodepsipeptide, cormycin A, produced in culture by the tomato pathogen Pseudomonas corrugata was elucidated by combined protein chemistry, mass spectrometry and two-dimensional NMR procedures. Its peptide moiety corresponds to L-Ser-D-Orn-L-Asn-D-Hse-L-His-L-aThr-Z-Dhb-L-Asp(3-OH)-L-Thr(4-Cl) [where Orn represents ornithine, Hse is homoserine, aThr is allo-threonine, Z-Dhb is 2,3-dehydro-2-aminobutanoic acid, Asp(3-OH) is 3-hydroxyaspartic acid and Thr(4-Cl) is 4-chlorothreonine], with the terminal carboxy group closing a macrocyclic ring with the hydroxy group of the N-terminal serine residue. This is, in turn, N-acylated by 3,4-dihydroxy-esadecanoate. In aqueous solution, cormycin A showed a rather compact structure, being derived from an inward orientation of some amino acid side chains and from the 'hairpin-bent' conformation of the lipid, due to inter-residue interactions involving its terminal part. Cormycin was significantly more active than the other lipodepsipeptides from Pseudomonas spp., as demonstrated by phytotoxicity and antibiosis assays, as well as by red-blood-cell lysis. Differences in biological activity were putatively ascribed to its weak positive net charge at neutral pH. Planar lipid membrane experiments showed step-like current transitions, suggesting that cormycin is able to form pores. This ability was strongly influenced by the phospholipid composition of the membrane and, in particular, by the presence of sterols. All of these findings suggest that cormycin derivatives could find promising applications, either as antifungal compounds for topical use or as post-harvest biocontrol agents.

The syringopeptins are a group of antimicrobial cyclic lipodepsipeptides produced by several plant-associated pseudomonads. A novel syringopeptin, SP508, was shown to be produced as two homologs (A and B) by Pseudomonas syringae pv. lachrymans strain 508 from apple and to structurally resemble syringopeptin SP22. SP508 differed from SP22 and other syringopeptins by having three instead of four ␣,␤-unsaturated amino acids and a longer ␤-hydroxy acyl chain. Both SP508 and SP22 displayed growth-inhibitory activities against Mycobacterium smegmatis, other gram-positive bacteria, and yeasts but not against gram-negative bacteria. Structure-activity analyses of the SP508 and SP22 homologs indicated chemical structural features that lead to enhanced antimycobacterial activity by these pseudomonad cyclic lipodepsipeptides.Syringopeptins (SPs) are bacterial secondary metabolites belonging to a class of cyclic lipodepsipeptides produced by certain pathovars of the plant bacterium Pseudomonas syringae (1,2,25,36). Their peptide portions contain either 22 (SP22) or 25 (SP25) amino acids that are predominantly hydrophobic, valine and alanine in particular. About 70% of the chiral residues are of the D configuration, and there are four ␣,␤-unsaturated and two 2,4-diaminobutyric acid residues (2,17,21,30). An N-terminal residue dehydroaminobutyric acid (Dhb) is N acylated by a 3-hydroxylated fatty acid chain containing either 10 or 12 carbon atoms; these two types of chains are designated A and B homologs and are typically the more abundant and less abundant forms, respectively. The C-terminal carboxyl group is esterified by the hydroxyl group of the allo-Thr residue positioned at the distance of 7 residues, thus forming an eightmembered lactone macrocycle. So far, two SP25 and three SP22 forms have been identified. SP25 is produced by P. syringae pv. syringae strains that have been isolated from infected millet (B359), citrus (B427) (2), and wheat (M1) (1) as well as from the wheat pathogen P. syringae pv. atrofaciens (36). An isoform differing in the C-terminal residue, SP25-Phe, was detected in a laurel-infecting strain (30). SP22 is produced by a P. syringae pv. syringae strain isolated from pear (B301) (2), and variants are produced by P. syringae pv. syringae strains from sugar cane (SP[SC]) (21) and bean (SPPhv) (17). Each SP-producing P. syringae strain produces one type of SP together with a smaller, nine-amino-acid-containing cyclic lipodepsipeptide-either syringomycin (13, 32), syringotoxin (3), syringostatin (13), or pseudomycin (5).The SPs are produced in infected plant tissues (12, 15), and they play roles as virulence factors in plant diseases (31). The phytotoxic physiological effects of the SPs were demonstrated with isolated plant mitochondria (10) and tobacco protoplasts (18). Lipid bilayer studies have revealed that the probable mechanism of action involves insertion into target membranes with formation of ion channels and consequent ion imbalances that lead to cell death (9, 18). In addition to their phyto...

Abstract:In this paper we report a comparative characterization of Small Unilamellar Vesicles (SUVs), Large Unilamellar Vesicles (LUVs) and Multilamellar Vesicles (MLVs) prepared from 1-palmitoyl-2-oleoyl-sn-glycero-3-phospatidylcholine (POPC), carried out using two NMR techniques, namely High Resolution NMR in solution and High Resolution-Magic Angle Spinning (HR-MAS). The size and size distributions of these vesicles were investigated using the dynamic light scattering technique. An improved assignment of the 1 H-NMR spectrum of MLVs is also reported.