Effect of lipid on the conformation of the N-terminal region of equinatoxin II: a synchrotron radiation circular dichroism spectroscopic study |
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Authors: | Alison Drechsler Andrew J Miles Raymond S Norton B A Wallace Frances Separovic |
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Institution: | (1) School of Chemistry, Bio21 Institute, University of Melbourne, Melbourne, VIC, 3010, Australia;(2) Department of Crystallography, Birkbeck College, University of London, London, WC1E 7HX, UK;(3) The Walter and Eliza Hall Institute of Medical Research, 1G Royal Parade, Parkville, VIC, 3052, Australia; |
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Abstract: | Equinatoxin II (EqtII) is a protein toxin that lyses both red blood cells and artificial membranes. Lysis is dependent on
the lipid composition, with small unilamellar vesicles (SUVs) of dimyristoylphosphatidylcholine (DMPC) and sphingomyelin (SM)
(1:1 molar) being lysed more readily than those of phosphatidylcholine alone. Removing the N-terminus of EqtII prevents pore
formation, but does not prevent membrane binding. A peptide corresponding to residues 1–32 of EqtII was found using NMR to
adopt a helical structure in micelles. To further understand the structural changes that accompany membrane insertion, synchrotron
radiation circular dichroism spectra of the N-terminal peptide in a range of model membranes have been analysed. The peptide
structure was examined in water, dodecylphosphocholine (DPC) and DPC:SM (5:1) micelles, and SUVs composed of dioleoylphosphatidylcholine
(DOPC) or DMPC, together with SM and cholesterol (Chol). The peptide adopted different conformations in different lipids.
Although the presence of SM did not affect the conformation in micelles, inclusion of SM in the bilayer-forming lipid increased
the helicity of the peptide. This effect was abolished when Chol was added in DOPC but not in DMPC, which may relate to liquid
ordered versus disordered phase properties of the lipid. SM may act as a promoter of membrane organisation necessary for membrane
lysis by EqtII. |
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