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Determining Structure and Composition of a Model Phospholipid Bilayer

Determining Structure and Composition of a Model Phospholipid Bilayer. ORANGE TEAM Monica Branco Suh Joon Han Matthew Helgeson Kathryn Krycka Jong Keun Park Chu Xiangiang. Phospholipid Bilayers. Phospholipid bilayers serve as biomimetic membranes

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Determining Structure and Composition of a Model Phospholipid Bilayer

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  1. Determining Structure and Composition of a Model Phospholipid Bilayer ORANGE TEAM Monica Branco Suh Joon Han Matthew Helgeson Kathryn Krycka Jong Keun Park Chu Xiangiang

  2. Phospholipid Bilayers • Phospholipid bilayers serve as biomimetic membranes • Lipids self-assemble into ordered, multi-layer structure • Our system: DMPC • Phospho-choline head group • C14 hydrocarbon chains

  3. Advanced Neutron Diffractometer/Reflectometer monitor Slit #1 Slit #2 sample q monocromator Slit #3 2q detector Slit #4 • Reflection of incident beam based on Bragg diffraction: ki kr Qz θ 2θ kt

  4. Experiment Objectives • Determine quantitative structural information • Bilayer thickness • Bilayer composition profiles • Solvent penetration • Extent of thermal fluctuation

  5. Sample Preparation • Deposition of lipid solution on glass slide • Solvent evaporation • Hydration of bilayer film in sample chamber (75% RH) • Allow for sample equilibration at 37ºC I(Q) Glass slide Q (Å-1)

  6. Determination of Bilayer Spacing 100% H2O 50/50 H2O/D2O 100% D2O • Phase problem: n=1 I(Q) n=2 Phospholipid bilayer spacing: d = 49.3 Å n=3 n=5 n=4 Q (Å-1)

  7. Solving the Phase Problem 100% H2O 50/50 H2O/D2O 100% D2O • Variation of solvent conditions: H2O  D2O I(Q) Q (Å-1)

  8. Scattering Length Density Profiles • SLD profiles for lipid C-H chains:

  9. Bilayer Composition Determination • Selective deuteration of solvent and lipid:

  10. Water and Hydrocarbon Profiles • Subtraction of profiles allows for identification of species profiles: VCH2=27 Å3 VCH3=54 Å3

  11. Conclusions • AND/R allows for detailed, quantitative structural and compositional characterization of biomimetic bilayers • Solving the phase problem • Selective contrast variation • Further experiments • Site-specific D-labeling • Protein incorporation

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