Determining Structure and Composition of a Model Phospholipid Bilayer

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

• Reflection of incident beam based on Bragg
  diffraction

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kr
Qz
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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
n1
I(Q)
n2
Phospholipid bilayer spacing d 49.3 Å
n3
n5
n4
Q (Å-1)

• Phase problem

7
Solving the Phase Problem

• 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

VCH227 Å3 VCH354 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