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The primary structure of some new lipodepsipeptides named syringopeptins, produced by plant pathogenic strains of Pseudomonas syringae pv. syringae has been determined by a combination of chemical methods, 'H and 13C NMR spectroscopy and FAB mass spectrometry. Two syringomycin-producingwith Tyr acylating aThr to form a macrolactone ring, and smaller amounts of the 3-hydroxydodccanoyl homologue. Evidence was obtained that a third syringomycin-producing strain and a syringotoxin-producing strain synthesize 3-hydroxydecanoyl-Dhb-Pro-Val-Ala-AlaVal-Leu-Ala-Ala-Dhb-Val-Dhb-Ala-Val-Ala-Ala-Dhb-aThr-Ser-Ala-Vnl~~Ala-Dab-Dab-Tyr, with Tyr and aThr forming again the macrolactone ring, and smaller amounts of the 3-hydroxydodecanoyl homologue.Phytotoxin; Lipodepsipeptide; Syringopeptin; Pseudomonas syringae pv. syringae

By a combination of 1D and 2D 1H-and ~3C-NMR, FAB-MS, and chemical and enzymatic reactions carried out at the milligram level, it has been demonstrated that syringomycin E, the major phytotoxic antibiotic produced by Pseudomonas syringae pv. syringae, is a new lipodepsipcptide. Its amino acid sequence is Ser-Ser-Dab-Dab-Arg-Phe-Dhb-4(Cl)Thr-3(OH)Asp with the fl-carboxy group of the C-terminal residue closing a macrocyclic ring on the OH group of the N-terminal Scr, which in turn is N-acylated by 3-hydroxydodecanoic acid. Syringomycins A~ and G, two other metabolites of the same bacterium, differ from syringomycin E only in their fatty acid moieties corresponding, respectively, to 3-hydroxydecanoic and 3-hydroxytetradecanoic acid.

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The covalent structure and most of the stereochemistry of the pseudomycins, bioactive metabolites of a transposon-generated mutant of a Pseudomonas syringae wild-type strain proposed for the biological control of Dutch ehn disease, have been determined. While two pseudomycins are identical to the known syringopeptins 25-A and 25-B, pseudomycins A, B, C, C' are new lipodepsinonapeptides. For all of these the peptide moiety-L-Thr(4-Cl) with the terminal carboxyl group closing a macrocyclic ring on the OH group of the N-terminal Ser. This is in turn N-acylated by 3,4dihydroxytetradecanoate in pseudomycin A, by 3-hydroxytetradecanoate in pseudomycin B, by 3,4-dihydroxyhexadecanoate in pseudomycin C, and by 3-hydroxyhexadecanoate in pseudomycin C'. Some preliminary data on the biological activity of pseudomycin A are reported.

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Pseudomonas syringae pv. syringae produces two groups of cyclic lipodepsipeptides (LDPs): the nona-peptides syringomycins, syringostatins, and syringotoxin (ST), and the more complex syringopeptins composed of either 22 or 25 amino acid residues (SP22 and SP25). Both classes of peptides significantly contribute to bacterial pathogenesis and their primary target of action seems to be the plasma membrane. We studied and compared the activity of some members of these two classes of LDPs on red blood cells and on model membranes (monolayers and unilamellar vesicles). All peptides induced red blood cell hemolysis. The mechanism was apparently that of a colloid-osmotic shock caused by the formation of pores, as it could be prevented by osmoticants of adequate size. Application of the Renkin equation indicated a radius of approximately 1 nm for the lesions formed by syringopeptins SP22A and SP25A, whereas those formed by syringomycin E (SRE) had a variable, dose-dependent size ranging from 0.7 up to 1.7 nm. All tested LDPs displayed surface activity, forming peptide monolayers with average molecular areas of 1.2 nm2 (SRE), 1.5 nm2 (SP22A), and 1.3 nm2 (SP25A). They also partitioned into preformed lipid monolayers occupying molecular areas that ranged from 0.6 to 1.7 nm2 depending on the peptide and the lipid composition of the film. These LDPs formed channels in lipid vesicles as indicated by the release of an entrapped fluorescent dye (calcein). The extent of permeabilization was dependent on the concentration of the peptide and the composition of the lipid vesicles, with a preference for those containing a sterol. From the dose dependence of the permeabilization it was inferred that LDPs increased membrane permeability by forming oligomeric channels containing from four to seven monomers. On average, syringopeptin oligomers were smaller than SRE and ST oligomers.