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 lipodepsipe ptides (LDPs): the nona-peptides syringomycins, syringostatins, and syringo toxin (ST), and the more complex syringopeptins composed of either 22 or 25 amino acid residues (SP22 and SP25), Both classes of peptides significantl y contribute to bacterial pathogenesis and their primary target of action s eems to be the plasma membrane. We studied and compared the activity of som e members of these two classes of LDPs on red blood cells and on model memb ranes (monolayers and unilamellar vesicles), All peptides induced red blood cell hemolysis, The mechanism was apparently that of a colloid-osmotic sho ck caused by the formation of pores, as it could be prevented by osmoticant s of adequate size, Application of the Renkin equation indicated a radius o f approximately 1 nm for the lesions formed by syringopeptins SP(22)A and S P(25)A, whereas those formed by syringomycin E (SRE) had a variable, dose-d ependent size ranging from 0.7 up to 1.7 nm, All tested LDPs displayed surf ace activity, forming peptide monolayers with average molecular areas of 1. 2 mm(2) (SRE), 1.5 nm(2) (SP(22)A), and 1.3 nm(2) (SP(22)A). They also part itioned into preformed lipid monolayers occupying molecular areas that rang ed from 0.6 to 1.7 nm2 depending on the peptide and the lipid composition o f the film, These LDPs formed channels in lipid vesicles as indicated by th e release of an entrapped fluorescent dye (calcein), The extent of permeabi lization was dependent on the concentration of the peptide and the composit ion 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 small er than SRE and ST oligomers.