Structure of the alamethicin pore reconstructed by x-ray diffraction analysis.
We reconstructed the electron density profile of the alamethicin-induced transmembrane pore by x-ray diffraction. We prepared fully hydrated multiple bilayers of alamethicin-lipid mixtures in a condition where pores were present, as established previously by neutron in-plane scattering in correlation with oriented circular dichroism. At dehydrated conditions, the interbilayer distance shortened and the interactions between bilayers caused the membrane pores to become long-ranged correlated and form a periodically ordered lattice of rhombohedral symmetry. To resolve the phase problem of diffraction, we used a brominated lipid and performed multiwavelength anomalous diffraction at the bromine K edge. The result unambiguously shows that the alamethicin pore is of the barrel-stave type consisting of eight alamethicin helices. This pore structure corresponds to the stable pores detected by neutron in-plane scattering in fully hydrated fluid bilayers at high peptide/lipid ratios, which are the conditions at which alamethicin was tested for its antibacterial activity.
Qian
Shuo
S
Department of Physics and Astronomy, Rice University, Houston, Texas 77251, USA.
Wang
Wangchen
W
Yang
Lin
L
Huang
Huey W
HW
D000408:Alamethicin / Q000737:chemistry*; D001966:Bromine / Q000737:chemistry; D018360:Crystallography, X-Ray; D008051:Lipid Bilayers / Q000737:chemistry; D008956:Models, Chemical; D010713:Phosphatidylcholines / Q000737:chemistry; D014961:X-Ray Diffraction
C513031:1,2-distearoyl(9-10-dibromo)-sn-glycero-3-phosphocholine; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D000408:Alamethicin; D001966:Bromine