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

The pore-forming activities of cyclic lipodepsipeptides (CLPs), syringopept in 22A (SP22A) and syringomycin E (SRE) were compared on the human red bloo d cell (RBC) membrane and on bilayer lipid membranes (BLMs). SP22A above a concentration of 4 x 10(5) molecules/cell significantly increased the RBC m embrane permeability for Rb-86. With electric current measurements on BLM, it was proved that like SRE, the SP22A formed two types of ion channels in the membrane, small and large, the latter having six times larger conductan ce and longer dwell time. Both CLPs formed clusters consisting of six small channels, and the channel-forming activity of SP22A is about one order of magnitude higher than that of SRE. A Hill coefficient of 2-3 estimated from the concentration dependence of th ese CLPs-induced lysis gave a proof of the pore oligomerization on RBCs. Tr ansport kinetic data also confirmed that SP22A pores were oligomers of at l east three monomers. While SRE pores were inactivated in time, no pore inac tivation was observed with SP22A. The Rb-86 efflux through SP22A-treated RB Cs approached the tracer equilibrium distribution with a constant rate; a c onstant integral current was measured on the BLM for as long as 2.5 h as we ll. The partition coefficient (K-p = 2 x 10(4) l/mol) between the RBC membr ane and the extracellular space was estimated for SRE to be at least six ti mes higher than that for SP22A. This finding suggested that the higher ion permeability of the SP22A-treated cells compared to that of SRE was the res ult of the higher pore-forming activity of SP22A. (C) 2000 Elsevier Science S.A. All rights reserved.