Abstract
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.
Original language | English |
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Pages (from-to) | 3512-3522 |
Number of pages | 11 |
Journal | Biophysical Journal |
Volume | 94 |
Issue number | 9 |
DOIs | |
State | Published - May 1 2008 |
Externally published | Yes |
Funding
This work was supported by National Institutes of Health Grant GM55203 and the Robert A. Welch Foundation Grant C-0991. The experiment was carried out in part at the National Synchrotron Light Source, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.