cholesterol structure in lipid rafts
DESCRIPTION
Cholesterol Structure in Lipid Rafts. Laura Toppozini CAP Congress 2014 June 19, 2014. Cholesterol in Lipid Membranes. Mosaic model: Lipids, cholesterol, and proteins homogeneously mixed. Singer and Nicholson, 1972. Lipid raft model: Cholesterol-rich domains. Simons, 1997. - PowerPoint PPT PresentationTRANSCRIPT
Laura ToppoziniCAP Congress 2014June 19, 2014
Cholesterol Structure in Lipid Rafts
Cholesterol in Lipid Membranes
Singer and Nicholson, 1972
Simons, 1997
Mosaic model:Lipids, cholesterol, and
proteins homogeneously mixed
Lipid raft model:Cholesterol-rich domains
What is cholesterol’s role in rafts?
Project Details
20,000- molecule simulations
• What is cholesterol’s role in lipid membranes?
• Can we see raft formation in a binary system?
• What can binary system rafts elucidate about rafts in biological membranes?
Neutron experiment at Canadian Neutron
Beam Centre
Coarse-grained MD simulations from collaborators at University of Mainz
Neutron diffraction with stacked,
oriented bilayers
L Toppozini, S Meinhardt, CL Armstrong, Z Yamani, N Kucerka, F Schmid, MC Rheinstadter. The Structure of Cholesterol in Lipid Rafts. Submitted, under review.
~40Å
20 mol%
~100Å
Liquid-ordered phase
Simulation: CG Molecular Dynamics
60 mol%
Liquid-ordered phase
Experiment: Neutron Scattering
supe
rres
olut
ion
{nm
ξ= λ2
∆ λ
Larger λ
Smaller λ
Cholesterol in Lipid Membranes
32.5% cholesterol Liquid–ordered phase
Selective Deuteration
Selectively highlight molecules
Cholesterol Structure
Cholesterol Structure
Liquid-DisorderedCholesterol-lipid
complexes
Umbrella model
Huang & Feigenson. Biophys J. 1999 76(4):2142-57
Cholesterol Structure
Cholesterol Plaques-Cholesterol bilayers/plaques
-Triclinic unit cella=b=12.8 Åα=95˚β=91.9˚γ=98.1˚
Ordered-Complexes-Ordered lipid-cholesterol complexes-Monoclinic unit cella=b= 11Åα= 131˚
Cholesterol Structures in Rafts
The liquid-ordered phase of a binary system is heterogeneous
Domains in binary systems may be nuclei which lead to rafts in biological membranes.
Small, (~10nm) transient (~100ns) structures are observed in lipid-cholesterol system
Observation of three coexisting cholesterol
structures in the lo phase:
Liquid disordered
Ordered lipid/cholesterol
Cholesterol plaques
Acknowledgements
Maikel C.RheinstadterClare ArmstrongNorbert KucerkaZahra YamaniSebastian MeinhardtFriederike Schmid
Lipid Structure
Liquid-disorderedfluid-like,
hexagonal lipid structure
Liquid-Ordered Rafts
Gel-like monoclinic lipid structure of
lipids in the rafts.
alipid-raft
blipid-raft
Simulations: changing chemical potential
Lipid/cholesterol phase diagram
Membranes, Rafts, and Scattering
~3000 bilayers/wafer give larger signals
Hydrated lipid bilayershave diffusive motion: signals are weak
• Typical neutron scattering setupgives large spatial averaging
• Gives bulk structure
• Are small structures being formed but averaged over?
Measurement of Rafts
neutron
Long coherence length
ξ
Short coherence length
ξ
ξ= λ2
∆ λ∝ √𝐸∆𝐸
wave package
ξξ
Condensation and the Umbrella Model
0Phospholipid head-group acts as umbrella, shields hydrophobic regions of cholesterol
0Cholesterol proximity suppresses tail fluctuations
0These complexes may form domains in lo phase at moderate cholesterol concentrations
Experiment: Neutron Scattering
0Change coherence length in-situ by changing wavelength
0Large ξ setup: averaging over large areas.
0Smaller ξ setup: integrates more efficiently over smaller structures