Neutron scattering in the plane of membranes: Structure of alamethicin pores

A technique of neutron in-plane scattering for studying the structures of peptide pores in membranes is described. Alamethicin in the inserted state was prepared in undeuterated and deuterated dilauroyl phosphatidylcholine (DLPC) hydrated with D2O or H2O. Neutron in-plane scattering showed a strong dependence on deuteration, clearly indicating that water is a part of the high-order structure of inserted alamethicin. The data are consistent with the simple barrel-stave model originally proposed by Baumann and Mueller. The theoretical curves computed with this model at four different deuteration conditions agree with the data in all cases. Both the diameter of the water pore and the effective outside diameter of the channel are determined accurately. Alamethicin forms pores in a narrow range of size. In a given sample condition, >70% of the peptide forms pores of n and n +/- 1 monomers. The pore size varies with hydration and with lipid. In DLPC, the pores are made of n = 8-9 monomers, with a water pore similar to 18 Angstrom in diameter and with an effective outside diameter of similar to 40 Angstrom. In diphytanoyl phosphatidylcholine, the pores are made of n approximate to 11 monomers, with a water pore similar to 26 Angstrom in diameter, with an effective outside diameter of similar to 50 Angstrom.