D. Di Giorgio

Novel bioactive lipodepsipeptides from Pseudomonas syringae: The pseudomycins

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 elm 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 corresponds to l‐Ser‐d‐Dab‐l‐Asp‐l‐Lys‐l‐Dab‐l‐aThr‐Z‐Dhb‐l‐Asp(3‐OH) ‐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 3,4‐dihydroxytetradecanoate 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.

The interaction of lipodepsipeptide toxins from Pseudomonas syringae pv. syringae with biological and model membranes : A comparison of syringotoxin, syringomycin, and two syringopeptins

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.

Corceptins, new bioactive lipodepsipeptides from cultures of Pseudomonas corrugata

© 1998 Federation of European Biochemical Societies.

Structure of fuscopeptins, phytotoxic metabolites of Pseudomonas fuscovaginae

The structure of the fuscopeptins, bioactive lipodepsipeptides produced in culture by the gramineae pathogen Pseudomonas fuscovaginae, has been determined. The combined use of FAB mass spectrometry, NMR spectroscopy and chemical and enzymatic procedures allowed one to define a peptide moiety corresponding to ZDhb‐DPro‐LLeu‐DAla‐DAla‐DAla‐DAlaDVal‐Gly‐DAla‐DVal‐DAla‐DVal‐ZDhb‐DaThr‐LAla‐LDabDDab‐LPhe with the terminal carboxyl group closing a macrocyclic ring on the hydroxyl group of the allothreonine residue. The N‐terminus is in turn acylated by 3‐hydroxyoctanoate in fuscopeptin A and 3‐hydroxydecanoate in fuscopeptin B. Some preliminary data on the biological activity of fuscopeptins are also reported.

Conductive Properties and Gating of Channels Formed by Syringopeptin 25A, a Bioactive Lipodepsipeptide from Pseudomonas syringae pv. syringae, in Planar Lipid Membranes

Syringopeptin 25A, a pseudomonad lipodepsipeptide, can form ion channels in planar lipid membranes. Pore conductance is around 40 pS in 0.1 M NaCl. Channel opening is strongly voltage dependent and requires a negative potential on the same side of the membrane where the toxin was added. These pores open and close with a lifetime of several seconds. At negative voltages, an additional pore state of around 10 pS and a lifetime of around 30 ms is also present. The voltage dependence of the rates of opening and closing of the stable pores is exponential. This allows estimation of the equivalent charge that is moved across the membrane during the process of opening at about 2.6 elementary charges. When NaCl is present, the pore is roughly 3 times more permeant for anions than for cations. The current voltage characteristic of the pore is nonlinear, i.e., pore conductance is larger at negative than at positive voltages. The maximal conductance of the pore depends on the concentration of the salt present, in a way that varies almost linearly with the conductivity of the solution. From this, an estimate of a minimal pore radius of 0.4 nm was derived.

Biological activities of pseudomycin A, a lipodepsinonapeptide from Pseudomonas syringae MSU 16H.

Similarly to other Pseudomonas lipodepsinonapeptides, pseudomycin A inhibits proton extrusion from maize roots, promotes closure of stomata in Vicia faba, necrosis of tobacco leaves, haemolysis of human erythrocytes, affects H(+)-ATPase activity and proton translocation in plasma membrane vesicles, and stimulates succinate respiration in pea mitochondria. In general, the biological activities of pseudomycin A are lower than those of syringomycin-E, the prototype member of this family of bacterial metabolities. This difference might depend on the diverse number and distribution of charged residues in the peptide moiety of these compounds.

Cercospora beticola toxin: a reassessment of some in vitro effects

Abstract In contrast to previous reports, highly purified samples of Cercospora beticola toxin (CBT), very effective in inhibiting phosphohydrolase activity and H+-transport in microsomal vesicles of maize roots, are unable to complete with tritium-labeled dihydrofusicoccin in binding to microsomal preparations of maize or spinach tissues.

Lipodepsipeptides From Pseudomonas syringae pv. syringae

The purification and structural characterization of phytotoxic lipodepsipeptides from some Pseudomonas syringae pv. syringae strains have been conducted in italy, USA and Japan during the past decade. The main results of the chemical investigations on these metabolites are reported in this paper together with some data of their biological activities.

A New Syringopeptin Produced by a Pseudomonas syringae Strain from Laurel

The major bioactive metabolites present in cultures of a Pseudomonas syringae pv. syringae strain isoialed from laurel are syringomycin E and syringopeptin 25-A. One of the minor metabolites is a new syringopeptin which differs from syringopeptin 25-A only for the occurrence of Phe instead of Tyr as C-terminal residue.

Studies on the Effect of Syringomycin and Syringopeptins on the Functions of Plant Mitochondria

The main Phytotoxins, syringomycin E and syringopeptins, isolated from cultures of Pseudomonas syringae pv. syringae strains, were separately tested for their effect on some mitochondrial functions. Syringopeptins were several times more active than syringomycin E in increasing succinate or NADH respiration and the ATPase activity; they aiso cause the membrane potential to collapse in isolated maize and pea mitochondria.