Solid-state NMR study of membrane interactions of the pore-forming cytolysin, equinatoxin II.
Equinatoxin II (EqtII) is a pore-forming protein from Actinia equina that lyses red blood cell and model membranes. Lysis is dependent on the presence of sphingomyelin (SM) and is greatest for vesicles composed of equimolar SM and phosphatidylcholine (PC). Since SM and cholesterol (Chol) interact strongly, forming domains or "rafts" in PC membranes, (31)P and (2)H solid-state NMR were used to investigate changes in the lipid order and bilayer morphology of multilamellar vesicles comprised of different ratios of dimyristoylphosphatidylcholine (DMPC), SM and Chol following addition of EqtII. The toxin affects the phase transition temperature of the lipid acyl chains, causes formation of small vesicle type structures with increasing temperature, and changes the T(2) relaxation time of the phospholipid headgroup, with a tendency to order the liquid disordered phases and disorder the more ordered lipid phases. The solid-state NMR results indicate that Chol stabilizes the DMPC bilayer in the presence of EqtII but leads to greater disruption when SM is in the bilayer. This supports the proposal that EqtII is more lytic when both SM and Chol are present as a consequence of the formation of domain boundaries between liquid ordered and disordered phases in lipid bilayers leading to membrane disruption.
School of Chemistry, Bio21 Institute, University of Melbourne, VIC 3010, Australia.
Alison
A
Drechsler
Gregor
G
Anderluh
Raymond S
RS
Norton
Frances
F
Separovic
D000818:Animals; D003064:Cnidarian Venoms / Q000737:chemistry* / Q000378:metabolism; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry* / Q000378:metabolism; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D008563:Membrane Lipids / Q000737:chemistry / Q000378:metabolism; D021962:Membrane Microdomains / Q000737:chemistry / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular; D054353:Perforin / Q000737:chemistry* / Q000378:metabolism; D044367:Phase Transition; D012615:Sea Anemones / Q000737:chemistry
D003064:Cnidarian Venoms; D008051:Lipid Bilayers; D008563:Membrane Lipids; D054353:Perforin; C012307:equinatoxin; D004134:Dimyristoylphosphatidylcholine