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Role of Sterols in Membranes: Cholesterol vs. Ergosterol & Lanosterol Dynamics Exploration

Explore the impact and dynamics of sterols like cholesterol, ergosterol, and lanosterol in membranes. Delve into their structural analysis, function, and interactions with lipids through simulations and experimental data.

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Role of Sterols in Membranes: Cholesterol vs. Ergosterol & Lanosterol Dynamics Exploration

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  1. Cholesterol vs. Ergosterol / Lanosterol in Membrane S(t)imulations Zoe Cournia 25 October 2004

  2. Overview • Motivation and Basics about Sterols in Membranes • Structural Analysis of the Membrane • Towards Understanding the Dynamics of the System… • Conclusions - Outlook

  3. The role of Cholesterol in the membrane • Regulates: • membrane fluidity • membrane permeability • lateral mobility of proteins Cholesterol ~40% in mammalian plasma membrane 18 enzymatic steps Ergosterol found in membranes of fungi and protozoans 9 enzymatic steps Lanosterol evolutionary precursor of cholesterol / ergosterol found in prokaryotes

  4. Cholesterol vs. Ergosterol & Lanosterol • Cholesterol • Saturated side chain • One hydrogen at C24 • One hydrogen at C14 • C5- C6 double bond • C7 – C8 single bond • C8 – C9 single bond • Ergosterol • Unsaturated side chain • One methyl at C24 • One hydrogen at C14 • C5- C6 double bond • C7 – C8 single bond • C8 – C9 double bond • Lanosterol • Unsaturated side chain • On hydrogen at C24 • One methyl at C14 • C5 – C6 single bond • C7 – C8 double bond • C8 – C9 double bond

  5. Determining why nature needs sterols • Why did nature select cholesterol for eukaryotic cells? • What is the role of cholesterol in plasma membranes? • Quasielastic neutron scattering (QENS) + MD simulations  dynamics of similar sterols in membranes (cholesterol, lanosterol, ergosterol) •  structure - function relationships of cholesterol + lipids

  6. Sterol-Lipid Phase Diagram • lipid-cholesterol: stable region of coexistence between ld-lo phases • at high concentrations  liquid-ordered phase (lo) • lipid-lanosterol: no lo formation  Cholesterol stabilizes the liquid-ordered phase Nielsen, Europhys.Lett., (2000) 52:368-374

  7. Systems + Simulation Details • Cholesterol/DPPC • - 28ns production run • Ergosterol/DPPC • - 10ns production run • Lanosterol/DPPC • - 1ns production run • Pure DPPC • - 10ns production run • General Characteristics • - PME, NPT • - 200 DPPC, 1600 H2O • - T = 309 K, P = 1atm • - 2ns equilibration (A) DPPC (B) Cholesterol (C) Ergosterol (D) Lanosterol

  8. Snapshots of the Lipid and Sterol in the Membrane Erg - DPPC Lan - DPPC Chol - DPPC

  9. Deuterium Order Parameters Chol/DPPC, Erg/DPPC, Lan/DPPC Pure DPPC z-axis In NMR: In Simulation:  C - H C - H C - H C - H

  10. Electron Density Profiles Pure DPPC Chol/DPPC, Erg/DPPC, Lan/DPPC h hpure-DPPC = 46.0 Å hCHOL-DPPC = 50.0 Å hERG-DPPC = 50.0 Å hLAN-DPPC = 49.0 Å X-Ray Franks, Chol-Dppc 40%mol, T = 24C

  11. Cholesterol / Ergosterol / Lanosterol Tilt Angle Avg. chol. tilt angle: 9.8°  5.1 Avg. erg. tilt angle: 8.6°  4.3 Avg. lan. Tilt angle: 15.5°  12.2 Smondyrev et al. (simulation): 10.6º (Chol-DMPC, 50%mol., T=50C) Smondyrev et al. (simulation): 22.2º (Chol-DMPC, 11%mol., T=50C)

  12. Radial Distribution Function Cholesterol OH – water O: 3 Ergosterol OH – water O: 2.5 Lanosterol OH – water O: 2

  13. Trans/Gauche Populations of DPPC Chains

  14. QENS study of the motion of cholesterol / ergosterol /lanosterol in DPPC bilayers Characteristics • 2 orientations: (a) membrane normal (z), (b) in the plane (x-y) • 3 energy resolutions (1, 8 and14eV)  three time scales • T = 20, 36, 50oC • 40% sterol concentration Results  motional anisotropy of cholesterol: long-range motions in the membrane normal: (a) out-of-plane diffusion parallel to membrane normal (for T  36oC cholesterol can move in opposite leaflets) (b) locally confined motion within the bilayer plane possible geometrical models Lateral/transversal diffusion rate: cholesterol > lanosterol > ergosterol Gliss, Bayerl et al., Biophys.J., 1999 / Endress et al, Biochemistry 2002

  15. Towards understanding the dynamics of the system… Center of mass motion in the z-direction 4ns, saved every 0.2ps Restricted diffusion Cholesterol: 2 types of motion: high amplitude/low amplitude Ergosterol: more confined motions Long-range diffusion

  16. movie

  17. Center of mass motion in the x-y plane (view from top) 4ns, saved every 1ps 2-6ns 6-10ns z-plane motion: long range ~10Ǻ (x-y)-plane motion: restricted ~4Ǻ

  18. Quasielastic Neutron Scattering

  19. QENS of Oriented Lipid Bilayers Scattering is Considered elastic: θ  θ 45º θ

  20. Outlook: Calculation of spectra  Calculation of EISF S(q,w=0) From QENS Experiment: EISF gives us information on the geometry of the motions

  21. Conclusions • Overall good agreement with experiment: Reproduced • structural and dynamical properties of the lipid/sterol systems • Cholesterol/Ergosterol induce order in the lipid bilayer / • Inhibit rotation of the middle carbons of the lipid acyl chain • Lanosterol has smaller ordering effect on the membrane / • Is located closed to the bilayer center • Two different types of diffusion for cholesterol/ergosterol: • long-range motions in the z-axis / restricted in x-y plane • Calculate lateral/transverse diffusion coeff. from MSD/QENS •  Geometrical models should be fitted to the EISF to • describe cholesterol motion (rotational, translational)

  22. Some Statistics for the end… A 100ps-trajectory = 630 MB Need 30ns  189 GB For my 4 systems, need: 189GB x 4 = 756 GB Solution?: Write DVDs 1 DVD = 4.3 GB I need to write 176 DVDs !!!! To write/read DVD ~1 hour Total time spent reading/writing: 176 hours Work hours: 4 hours/day Total working days of reading(once!)/writing: 44 days !!!

  23. CMB Teufelskreis Problem !!

  24. Thanks !!! … and Special Thanks to: Jeremy Matthias Vandana Torsten Lars Emil Endress Bogdan Alex

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