Martin I, Epand R M, Ruysschaert J M
Laboratoire de Chimie-Physique des Macromolécules aux Interfaces (LCPMI), CP206/2, Université Libre de Bruxelles, 1050 Brussels, Belgium.
Biochemistry. 1998 Dec 1;37(48):17030-9. doi: 10.1021/bi980909i.
We recently demonstrated that a peptide representing the putative fusion domain of fertilin, a surface membrane protein of sperm involved in sperm-egg fusion, induces fusion of large unilamellar vesicles containing negatively charged lipids [Martin, I., and Ruysschaert, J. M. (1997) FEBS Lett. 405, 351-355]. In the present work, we demonstrate that increasing the concentration in negatively charged lipids strongly enhances the binding of the fertilin fusion peptide to the membrane, suggesting that electrostatic attractions play a crucial role in the binding process. While no significant change of the secondary structure content is observed by increasing the amounts of negatively charged lipids in the bilayer, the orientation of the alpha-helix changes from a parallel to an oblique orientation in the membrane. This topological change is confirmed by amide II hydrogen/deuterium exchange measurements that monitor the accessibility of the peptide to the water medium. Differential scanning calorimetry data also suggest that the fertilin fusion peptide lowers the bilayer to hexagonal phase transition temperature of model membranes composed of mixtures of dipalmitoleoylphosphatidylethanolamine and 1-palmitoyl-2-oleoylphosphatidylserine and therefore promotes negative curvature in lipid vesicles. A comparison of the biophysical properties and the membrane-perturbing activities of fertilin and of viral fusion peptides is discussed in terms of sperm-egg fusion and virus cell fusion.
