1Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ, USA 2Department of Physics, Indian Institute of Science, Bangalore, India

3Department of Physics, University of Arizona, Tucson, AZ, USA

Soohyun K. Lee1, Trivikram R. Molugu1, K.J. Mallikarjunaiah1,2, Michael F. Brown1,3

Elastic Deformation And Collective Dynamics in Lipid Membranes: A Solid-state 2H

NMR Relaxation Study

BPS platform talk 20163/1/2016, 4:00 PM

J.J. Kinnun et al. (2015) BBA 1848, 246

How Does Hydration Affect Lipid Membranes And

Dynamics?

How Does Hydration Affect Lipid Membranes And Dynamics?

Parsegian: X-ray diffraction - bilayer thickness increases with decrease in water level

Nagle: X-ray diffraction and diatometry Gawrisch: X-ray diffraction and infrared

measurements – bilayer thickness also changes with polyunsaturated lipids

Mallikarjunaiah: Solid-state 2H NMR - bilayer thickness is very sensitive to the hydration levels

Lets examine the membrane from the dynamics standpoint!

K.J. Mallikarjunaiah et al. (2011) Biophys. J. 100, 98

• Introduction to solid-state 2H NMR experiments

• Model-free interpretation of lipid relaxation data

• Collective lipid dynamics

• Hydration-induced slow dynamics

• Conclusions

Outline of the Talk

J.J. Kinnun et al. (2015) BBA 1848, 246K.J. Mallikarjunaiah et al. (2011) Biophys. J. 100, 98

• Introduction to solid-state 2H NMR experiments

• Model-free interpretation of lipid relaxation data

• Collective lipid dynamics

• Hydration-induced slow dynamics

• ConclusionsJ.J. Kinnun et al. (2015) BBA 1848, 246K.J. Mallikarjunaiah et al. (2011) Biophys. J. 100, 98

Outline of the Talk

• Line shape measurements– Reveal motional amplitudes– Gives structural information

like in X-ray crystallography• Relaxation measurements– Depends on motional

amplitudes and rates– Informative on molecular

motions over a wide frequency range

Solid-state 2H NMR Experiments Are Done in Two Ways

A. Leftin et al. (2014) eMagRes 3, 199X. Xu et al. (2014) eMagRes 3, 275

• Line shape measurements– Reveal motional amplitudes– Gives structural information

like in X-ray crystallography• Relaxation measurements– Depends on motional

amplitudes and rates– Informative on molecular

motions over a wide frequency range

Solid-state 2H NMR Experiments Are Done in Two Ways

A. Leftin et al. (2014) eMagRes 3, 199X. Xu et al. (2014) eMagRes 3, 275

A. Leftin, M.F. Brown (2011) BBA 1808, 818

Solid-state 2H NMR Gives Site-resolved Information for Bilayers

J.J. Kinnun et al. (2015) BBA 1848, 246

Solid-state 2H NMR Gives Site-resolved Information for Bilayers

Closure Property of Reference Frames in Solid-state 2H NMR Experiment

A. Leftin et al. (2014) eMagRes 3, 199X. Xu et al. (2014) eMagRes 3, 275

A. Leftin et al. (2013) JMB 425, 2973A. Leftin et al. (2011) BBA 1808, 818

Hierarchy of Membrane Dynamics

Molecular motions near the Larmor frequency contribute to Relaxation NMR relaxation methods are suitable to probe such dynamics.

Motions Collective Motions

(b)

(c)

NMR Relaxation Experiments(a)

Quadrupolar echo-T2

T1 inversion recovery

CPMG-T2

A. Leftin et al. (2011) BBA 1808, 818X. Xu et al. (2014) eMagRes 3, 275

• Introduction to solid-state 2H NMR experiments

• Model-free interpretation of lipid relaxation data

• Collective lipid dynamics

• Hydration-induced slow dynamics

• Conclusions

Outline of the Talk

J.J. Kinnun et al. (2015) BBA 1848, 246K.J. Mallikarjunaiah et al. (2011) Biophys. J. 100, 98

Model-free Interpretation of Lipid Relaxation Data

Gateway to discoveries on membrane motions

Relaxation Measurements Are Related to Quasi-elastic

Properties

• D is the viscoelastic property, the lower the stiffer (Viscosity is and K is the elastic constant)

• The linear dependence is due to the slow collective dynamics• Assumptions are that the sample is large vesicles and motions are of

bilayer dimension

X. Xu et al. (2014) eMagRes 3, 275

G.V. Martinez et al. Phys. Rev. E (2002) 66 050902

M.F. Brown (1984) JCP 80, 2832A.A. Nevzorov & M.F. Brown (1997) JCP 107, 10288

Order Fluctuations & Elastic Membrane Deformation

3D membrane deformation model:

2D flexible surface model:

Free membrane limit (l < t < d)

Strongly coupled limit (t << d < l)

Free membrane limit (t << l < d)

3D quasi-elastic deformations (Brown)

smectic undulations (Blinc) peristaltic fluctuations

free planar membrane (Marqusee;Kothe; Blinc)

Vesicle shape fluctuations (Vilfan; Kothe)

• Introduction to solid-state 2H NMR experiments

• Model-free interpretation of lipid relaxation data

• Collective lipid dynamics

• Hydration-induced slow dynamics

• Conclusions

Outline of the Talk

J.J. Kinnun et al. (2015) BBA 1848, 246K.J. Mallikarjunaiah et al. (2011) Biophys. J. 100, 98

A. Leftin et al. (2011) BBA 1808, 818

Effect of Head Group on Membrane

Elasticity

• Linear square-law plot shows presence of collective dynamics

• For a given lipid, slope of the square-law plot is temperature independent

• The thermal energy is spent on structural perturbation

• Elastic properties do not change in liquid-crystal phase upon heating

Effect of Temperature on Membrane Structure And

Elasticity

A. Leftin et al. Biophys. J. (2014) 107, 2274 A. Leftin et al. J. Mol. Biol. (2013) 425, 2973

R1Z / s−1

45

• Correspondence of NMR observables with material properties

• Progressive increase in bilayer stiffness with increasing sterol content

• Emergence of bilayer elasticity over atomistic distances!

• Evolution of biophysical function?

Bending Energies Deduced from

2H NMR Spin–lattice Relaxation

M.F. Brown et al. (2001) Phys. Rev. E 64, 010901G.V. Martinez et al. (2002) Phys. Rev. E 66, 050902

Outline of the Talk

J.J. Kinnun et al. (2015) BBA 1848, 246K.J. Mallikarjunaiah et al. (2011) Biophys. J. 100, 98

• Introduction to solid-state 2H NMR experiments

• Model-free interpretation of lipid relaxation data

• Collective lipid dynamics

• Hydration-induced slow dynamics

• Conclusions

Outline of the Talk

J.J. Kinnun et al. (2015) BBA 1848, 246K.J. Mallikarjunaiah et al. (2011) Biophys. J. 100, 98

• Introduction to solid-state 2H NMR experiments

• Model-free interpretation of lipid relaxation data

• Collective lipid dynamics

• Hydration-induced slow dynamics

• Conclusions

Spin-lattice Relaxation Rates Indicate Collective Order-director

FluctuationsDMPC-d54

A. Leftin et al. (2013) J. Mol. Biol 425, 2973A. Leftin et al. (2014) Biophys. J. 107, 2274

Spin-Lattice Relaxation Rates Indicate Collective Dynamics in

Membrane Lipids

POPC-d31

• Segmental order parameters and spin-lattice relaxation rates follow a theoretical square-law functional dependence

• Temperature independent square-law plots indicate collective membrane dynamics similar to nematic liquid-crystals

R1Z / s−1

R1Z / s−1

• Undulatory motion gets more prominent at higher hydration• Square-law breaking

near the head group is due to penetration of water into the lipid

Hydration Mediated Ultra-slow Dynamics in Lipid Membranes

H2O

K.J. Mallikarjunaiah et al. (2011) Biophys. J. 100, 98A. Leftin, T.R. Molugu (2014) Biophys. J. 107, 2274

50302010

R2 / s−1

Outline of the Talk

J.J. Kinnun et al. (2015) BBA 1848, 246K.J. Mallikarjunaiah et al. (2011) Biophys. J. 100, 98

• Introduction to solid-state 2H NMR experiments

• Model-free interpretation of lipid relaxation data

• Collective lipid dynamics

• Hydration-induced slow dynamics

• Conclusions

• Liquid-crystalline phospholipids showed temperature independent elastic property.

• Chain length of disaturated phospholipid membranes weakly affected elasticity.

• Phosphoethanolamine membranes were stiffer than phosphocholine membranes, should be a consequence of the molecular packing.

• Membrane hydration showed a significant effect on elastic properties.

• High values for transverse relaxation rates indicated ultra-slow collective dynamics.

• Square-law breaking at high hydration should be the consequence of excess water penetrating into bilayer core.

• Membrane dehydration, addition of cholesterol, osmolytes, consistently showed stiffening effect on membranes

• Square-law connected the microscopic segmental dynamics to the macroscopic membrane properties.

Biophysical Conclusions

X. Xu et al. (2014) eMagRes 3, 275J.J. Kinnun et al. (2015) BBA 1848, 246

Andrey Struts

Acknowledgements

Xiaolin Xu

Rami Musharrafieh

Udeep Chawla

Soohyun Lee

Suchi Perera

Michael Brown Michael PitmanVikram Molugu

THANK YOU ALL!Amanda Johnson