Structure of Peptide-Induced Transmembrane Pore Determined by Anomalous X-Ray Diffraction

Abstract

We determined the structure of the melittin-induced transmembrane pore by X-ray diffraction. The multibilayer sample on substrate was prepared in full hydration. The peptide-to-lipid ratio, P/L, of the melittin-lipid mixtures were in the condition where pores were present, as established previously by neutron in-plane scattering in correlation with oriented circular dichroism. At low hydration levels, the interbilayer distance shortened and caused the membrane pores to become long-ranged correlated and form a periodically ordered lattice of rhombohedral symmetry. Here we used the multiwavelength anomalous dispersion (MAD) method to solve the phase problem for a rhombohedral phase of a phospholipid with brominated chains and performed multiwavelength anomalous diffraction at the bromine K edge. The X-ray light source in BL23A beam line of NSRRC and home-made humidity-temperature controlled chamber will be applied in the measurements. We found the melittin-induced pores were at least partially framed by a lipid monolayer. Evidence suggests that the pore structure is of the toroid type different from the barrel-stave type induced by alamethicin.