Diffraction from Bilayers

Abstract

X‐ray diffraction provided a direct proof for the hypothesis that the basic structural element of biological membranes is a bimolecular layer of phospholipid molecules. Diffraction from peptide–lipid mixtures can be used to study a great variety of membrane problems.

Keywords: lamellar diffraction; in‐plane scattering; phospholipid bilayers; peptide lipid interactions; hydrophobic matching

Figure 1.

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

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., ). (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., .)

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., and Lee et al., ).

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., .)

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., .)

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, .)

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References

Harroun TA, Heller WT, Weiss TM, Yang L and Huang HW (1999) Experimental evidence of hydrophobic matching and membrane‐mediated interactions in lipid bilayers containing gramicidin. Biophysical Journal 76: 937–945.

He K, Ludtke SJ, Worcester DL and Huang HW (1996) Neutron scattering in the plane of membrane: structure of alamethicin pores. Biophysical Journal 70: 2659–2666.

Huang HW, Chen FY and Lee MT (2004) Molecular mechanism of peptide‐induced pores in membranes. Physical Review Letters 92: 198304(1–4).

Levine YK and Wilkens MHF (1971) Structure of oriented lipid bilayers. Nature New Biology 230: 69–72.

Olah GA, Huang HW, Liu W and Wu Y (1991) Location of ion binding sites in the gramicidin channel by x‐ray diffraction. Journal of Molecular Biology 218: 847–858.

Smith GS, Sirota EB, Safinya CR, Plano RJ and Clark NA (1990) X‐ray structural studies of freely suspended ordered hydrated DMPC multimembrane films. Journal of Chemical Physics 92: 4519–4529.

Weiss TM, van der Wel PCA, Killian JA, Koeppe II RE and Huang HW (2003) Hydrophobic mismatch between helices and lipid bilayers. Biophysical Journal 84: 379–385.

Wilkens MHF, Blaurock AE and Engelman DM (1971) Bilayer structure in membranes. Nature New Biology 230: 72–76.

Yang L, Weiss TM and Huang HW (2000) Crystallization of antimicrobial pores in membranes: magainin and protegrin. Biophysical Journal 79: 2002–2009.

Yang L and Huang HW (2002) Observation of a membrane fusion intermediate state. Science 297: 1877–1879.

Further Reading

Lee MT, Chen FY and Huang HW (2004) Energetics of pore formation induced by membrane active peptides. Biochemistry 43: 3590–3599.

Franks NP and Lieb WR (1979) The structure of lipid bilayers and the effects of general anaesthetics. Journal of Molecular Biology 133: 469–500.

Tardieu A, Luzzati V and Reman FC (1973) Structure and polymorphism of the hydrocarbon chains of lipids: a study of lecithin‐water phases. Journal of Molecular Biology 75: 711–733.

Yang L, Weiss TM, Harroun TA, Heller WT and Huang HW (1999) Supramolecular structures of peptide assemblies in membranes by neutron off‐plane scattering: method of analysis. Biophysical Journal 77: 2648–2656.

Yang L, Harroun TA, Weiss TM, Ding L and Huang HW (2001) Barrel‐stave model or toroidal model? A case study on melittin pores. Biophysical Journal 81: 1475–1485.

Yang L and Huang HW (2003) A rhombohedral phase of lipid containing a membrane fusion intermediate structure. Biophysical Journal 84: 1808–1817.

Zasloff M (2002) Antimicrobial peptides of multicellular organisms. Nature 415: 389–395.

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Huang, Huey W(Jan 2006) Diffraction from Bilayers. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0003941]