Figure 1. Ion-binding sites of the gramicidin channel. (a) Normalized electron density profiles, , of gramicidin/DLPC bilayers with Tl⁺ (dotted line) and without salt (solid line). (b) Difference electron density profile (Tl⁺)–(salt free). (c) of gramicidin/DLPC bilayers with Ba²⁺ (dotted line) and with Mg²⁺ (solid line). (d) Difference profile (Ba²⁺)–(Mg²⁺). (Reproduced from Olah et al., 1991.)

Figure 2. Hydrophobic matching between lipids and peptides. (a) PtP of DMPC bilayers and DMPC bilayers containing gramicidin (gD) at 1:10 peptide/lipid molar ratio as a function of lamellar spacing D at specified temperatures (reproduced from Harroun et al., 1999). (b) PtP of pure lipid bilayers and bilayers containing WALP at 1:20 peptide/lipid molar ratio as a function of lamellar spacing D. The WALP density is the same as that of gramicidin channels, since the latter are dimers. The temperature of measurement was 35°C for DMPC, and 30°C for DLPC and DTPC. (Reproduced from Weiss et al., 2003.)

Figure 3. Examples of membrane thickness measured as a function of the peptide concentration P/L. The hydrocarbon thickness h is PtP minus 1 nm (twice the phosphate to chain distance). Data of six different peptide/lipid systems are shown: alamethicin in diphytanoyl phosphatidylcholine (DPhPC), alamethicin in a mixture of dioleoyl phosphatidylcholine (DOPC) and dioleoyl phosphatidylethanolamine (DOPE), melittin in DPhPC, melittin in DOPC, melittin in palmitoyl-oleoyl phosphatidylcholine (POPC), and melittin in dieicosenoyl phosphatidylcholine (DiC20:1PC). The arrows indicate the threshold P/L* that were independently measured by detecting a change of peptide orientation upon the onset of pore formation (reproduced from Huang et al., 2004 and Lee et al., 2004).

Figure 4. Radial distribution functions of gramicidin obtained from the in-plane scattering intensities of gramicidin embedded in DLPC and DMPC bilayers at specified temperatures. The position of the first peak gives the most probable nearest-neighbour separation between gramicidin channels in the bilayer. (Reproduced from Harroun et al., 1999.)

Figure 5. Neutron in-plane scattering intensity of alamethicin pores in DLPC bilayer at P/L=1/10 hydrated with  D₂O (data +) or with  H₂O (data o). The broken line is a simulated structure factor of hard disks in two dimensions. The dotted line is the square of the form factor for the pore. The solid line is the product of last two that fits the intensity curve. (Reproduced from He et al., 1996.)

Figure 6. Structure of a fusion intermediate. (Left) Diffraction pattern from partially dehydrated multiple bilayers of diphytanoyl phosphatidylcholine. (Right) The electron density distribution constructed from the diffraction pattern shows an interbilayer structure called a stalk. (Reproduced from Yang and Huang, 2002.)