Membrane-permeabilizing activities of cyclic lipodepsipeptides, syringopeptin 22A and syringomycin E from Pseudomonas syringae pv. syringae in human red blood cells and in bilayer lipid membranes

Channel-forming activity of syringopeptin 25A in mercury-supported phospholipid monolayers and negatively charged bilayers

“…In the light of the above results on SP25A ion-channel activity, as reported by us [15] at a DPTL/DOPC tBLM and by others [11,13,14] at conventional BLMs, the following conclusions can be reasonably drawn about the charge transient behavior of this lipodepsipeptide at a DPTL/ DOPS tBLM. The fact that the maximum limiting height of the charge transient plateau amounted to − 45 ± 5 μC cm −2 denotes that the SP25A ion channel is closed at the initial potential E i = −0.30 V, and hence does not allow Cl − inflow.…”

“…15. This interaction, followed by peptide insertion and pore formation into the corresponding membrane according to the mechanism reported before [11][12][13][14], might possibly justify the reported antimicrobial selectivity of this lipodepsipeptide.…”

“…The existence of both large and small SP25A ion channels was assumed on the basis of the detection of both large and small single-channel conductance fluctuations in SP25A single channel measurements at conventional BLMs [11,13,14]. Since the small fluctuations were found to be exactly one fourth of the large ones, Dalla Serra et al [13] assumed that the large channels result from the tetrameric aggregation of the small channels, leading to their synchronous opening and closing, in analogy with the hexameric clusters proposed for syringomycin E [42].…”

“…NMR investigations in aqueous solution showed that SP25A assumes a conformation having distinct structural portions, e.g. a loop region (amino acids 2-6), a left-handed helical region (amino acids [8][9][10][11][12][13][14][15], and an octadepsipeptide moiety (amino acids [18][19][20][21][22][23][24][25] that resembles the seam of a tennis ball [3,4]. Syringopeptins have phytotoxic, antifungal and antibacterial properties.…”

“…Differently from SR, which presents an increased activity on phospholipid vesicles in the presence of sterols, syringopeptins do not require the latter molecules to elicit their potential. Measurements of single-and multi-channel currents induced by syringopeptins at conventional bilayer lipid membranes (BLMs) have been performed by different groups [11][12][13][14]. Both small and large single-channel conductance fluctuations were observed, which present a 4-6 fold difference in their level of conductance and in the corresponding open state lifetime [11,13,14].…”