title: Peptide-induced bilayer thinning structure of unilamellar vesicles and the related binding behavior as revealed by X-ray scattering.
abstract: We have studied the bilayer thinning structure of unilamellar vesicles (ULV) of a phospholipid 1,2-dierucoyl-sn-glycero-3-phosphocholine (di22:1PC) upon binding of melittin, a water-soluble amphipathic peptide. Successive thinning of the ULV bilayers with increasing peptide concentration was monitored via small-angle X-ray scattering (SAXS). Results suggest that the two leaflets of the ULV of closed bilayers are perturbed and thinned asymmetrically upon free peptide binding, in contrast to the centro-symmetric bilayer thinning of the substrate-oriented multilamellar membranes (MLM) with premixed melittin. Moreover, thinning of the melittin-ULV bilayer associates closely with peptide concentration in solution and saturates at ~4%, compared to the ~8% maximum thinning observed for the correspondingly premixed peptide-MLM bilayers. Linearly scaling the thinning of peptide-ULV bilayers to that of the corresponding peptide-MLM of a calibrated peptide-to-lipid ratio, we have deduced the number of bound peptides on the ULV bilayers as a function of free peptide concentration in solution. The hence derived X-ray-based binding isotherm allows extraction of a low binding constant of melittin to the ULV bilayers, on the basis of surface partition equilibrium and the Gouy-Chapman theory. Moreover, we show that the ULV and MLM bilayers of di22:1PC share a same thinning constant upon binding of a hydrophobic peptide alamethicin; this result supports the linear scaling approach used in the melittin-ULV bilayer thinning for thermodynamic binding parameters of water-soluble peptides.
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
authors.forename: Chun-Jen
authors.initials: CJ
authors.lastname: Su
authors.forename: Shiuan-Shiaou
authors.initials: SS
authors.lastname: Wu
authors.forename: U-Ser
authors.initials: US
authors.lastname: Jeng
authors.forename: Ming-Tao
authors.initials: MT
authors.lastname: Lee
authors.forename: An-Chung
authors.initials: AC
authors.lastname: Su
authors.forename: Kuei-Fen
authors.initials: KF
authors.lastname: Liao
authors.forename: Wei-Yu
authors.initials: WY
authors.lastname: Lin
authors.forename: Yu-Shan
authors.initials: YS
authors.lastname: Huang
authors.forename: Chun-Yu
authors.initials: CY
authors.lastname: Chen
mesh_terms: D000408:Alamethicin / Q000737:chemistry; D001703:Biophysics / Q000379:methods*; D005583:Fourier Analysis; D008051:Lipid Bilayers / Q000737:chemistry*; D008555:Melitten / Q000737:chemistry*; D015233:Models, Statistical; D010455:Peptides / Q000737:chemistry*; D011485:Protein Binding; D012542:Scattering, Radiation; D053838:Scattering, Small Angle; D013816:Thermodynamics; D053835:Unilamellar Liposomes / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction / Q000379:methods; D014965:X-Rays
chemical_list: D008051:Lipid Bilayers; D010455:Peptides; D053835:Unilamellar Liposomes; D014867:Water; D008555:Melitten; D000408:Alamethicin