Assessing the Nature of Lipid Raft Membranes

Perttu Niemelä Laboratory of Physics and Helsinki Institute of Physics,

Helsinki University of Technology

GROMACS workshopCSC, Espoo, 28 February 2007

Introduction: Lipids

Introduction: SM-SM Interactions

OH-group involved withintramolecular h-bonding

NH-group involved withintermolecular h-bonding

Phosphoryl oxygens involvedwith H20 hydrogen bonding

Niemelä, Hyvönen, Vattulainen (2004) Biophys J, 87:2976 – 2989Niemelä, Hyvönen, Vattulainen (2006) Biophys J, 90:851 – 863

Introduction: CHOL-SM

Aittoniemi, Niemelä, Hyvönen, Karttunen, Vattulainen (2007) Biophys J, 92:1125-1137.

Introduction: Bilayer Phases

Liquiddisordered

Gel Liquid ordered

Traffic, 5 (2004) 241 - 246

Introduction: Domains

http://www.memphys.sdu.dk

http://www.memphys.sdu.dk

Sphingomyelin (SM) + Cholesterol

Phosphatidyl-choline (PC)

de Almeida et al, Biophys. J. 85:2406-2416 (2003)Hancock et al, Nat Rev Mol Cell Biol 7:456-462

< 25 nm

75-100 nm25-75 nm

Introduction: Rafts in Vivo

Schuck et al (2004) J Cell Sci, 117:5955-5964.

Introduction: Rafts in Vivo

Lipid Mixtures

POPC:SM:CHOL 1:1:1

POPC:SM:CHOL 2:1:1

POPC:SM:CHOL 62:1:1

Niemelä, Ollila, Hyvönen, Karttunen, Vattulainen, PLoS Comp Biol (2007) 3:e34.

Simulation Details:• 1024 lipids / system• ~ 30 waters/lipid• time-step 2 fs• simulation length 50-100 ns• T = 310 K (Nose-Hoover)• p = 1 atm (Parrinello-R.)• = 0 (PN = PL)• periodic boundaries

Lipids:• Force fields previously validated• OPLS/Berger-97 (lipid.itp) + GROMOS• United atoms for CH2/CH3• Explicit hydrogens for NH/OH• SPC-waterNiemelä, Ollila, Hyvönen, Karttunen, Vattulainen, PLoS Comp Biol (2007) 3:e34.

Equilibration: Area per lipid

Kucerka et al., J. Membr. Biol (2005) 208:193; Hofsäss et al., Biophys. J. (2003) 84:2192

X-ray diffractionPOPC: 0.683 ± 0.015 nm2

MD-simulationDPPC-CHOL 25%0.48 nm2

MD-simulationDPPC-CHOL 40%0.43 nm2

Acyl Chain Ordering

Cn

Cn-1

Cn+1

z

molCD

mol

SS

S

2

1

1cos32

1 2

Lateral DiffusionPOPC:PSM:CHOL DT [10-7 cm2/s]

1:1:1 0.037 ± 0.002

2:1:1 0.08 ± 0.02

62:1:1 0.67 ± 0.06t

tr

dD

tT

)(

2

1lim

2

Filippov et al, Biophys J (2006) 90:2086.

Experiment PFG-NMR: DOPC:PSM:CHOL (10% - 30% CHOL)

DT1 1.0 * 10-7 cm2/sDT2 0.1 * 10-7 cm2/s

Bilayer ThicknessPOPC:PSM:CHOL d [nm]

1:1:1 4.40 ± 0.05

2:1:1 4.29 ± 0.05

62:1:1 3.53 ± 0.05

d = 0.6 nm ... 0.9 nm

Membrane undulations

Lindahl and Edholm., Biophys J, 79 (2000) 426 - 433

)(),( quyxu undund

Undulatory Spectrum

62:1:1

2:1:1

1:1:1

4 qy

Niemelä, Ollila, Hyvönen, Karttunen, Vattulainen, PLoS Comp Biol (2007) 3:e34.

Elastic Properties

Rawicz et al (2000) Biophys J. 79:328; Evans et al. (1990) PRL 64:2094; Needham et al (1990) 58:997; Henriksen et al (2004) Eur Biophys J 33:732

POPC:PSM:CHOL kc [10-20 J] experimental

1:1:1 10 ± 2 120-170% increase, POPC-CHOL (30-50)%2:1:1 7 ± 2

62:1:1 6 ± 2 4 to 9 * 10-20 J

POPC:PSM:CHOL KA [10-3 N/m] experimental

1:1:1 2700 ± 700 1700 (SM:CHOL)

2:1:1 1000 ± 400 780 (PC:CHOL)

62:1:1 200 ± 100 140-300 (PC)

Pressure Profiles

),,(1

)( jiijji

ijislicei

iilocal zzzfmV

z rFvvp

Lindahl et al. , J. Chem. Phys, 113 (2000) 3882-3893

z

0)( dzz

)()()( zPzPz LN

Pressure Profiles

Niemelä, Ollila, Hyvönen, Karttunen, Vattulainen, PLoS Comp Biol (2007) 3:e34.

Lipid-Protein Interactions

R. Cantor, J. Phys. Chem. (1997) 101, 1723-1725

Lipid-Protein Interactionsz

CLOSED

OPEN

Gullingsrud et. al., Biophys J, 86 (2004) 3496-3509

MscL

Lipid-Protein Interactions

dzzAzpW )()(

Mechanical work to create protein-shaped cavity

Work to close one MscL channel in lipid bilayer:

openclosed WWW

Gullingsrud et. al., Biophys J, 86 (2004) 3496-3509

Lipid-Protein Interactions

Work to open MscL in different membrane environments:

POPC:PSM:CHOL W [kBT]

1:1:1 11 2

2:1:1 4 1

1:0:0 1.9 0.2

0:1:0 1.0 0.6

1:0:1 (DPPC) 1.0 0.4

Niemelä, Ollila, Hyvönen, Karttunen, Vattulainen, PLoS Comp Biol (2007) 3:e34.

Summary• Increased SM and CHOL concentration leads to

ordered, rigid and slow bilayers

• Pressure profiles in raft and non-raft mixtures differ -> effects on proteins?

Acknowledgements• Other people involved:

• BIO-group at COMP, Helsinki Univ. of Tech.

• Academy of Finland

• CSC, the Finnish IT center for science

• SDU supercluster (Odense, Denmark)

Ilpo Vattulainen Mikko Karttunen Jussi Aittoniemi Marja Hyvönen Samuli Ollila

Peristaltic Spectrum