slide1 n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Interactions between lipid membranes PowerPoint Presentation
Download Presentation
Interactions between lipid membranes

Loading in 2 Seconds...

play fullscreen
1 / 48

Interactions between lipid membranes - PowerPoint PPT Presentation


  • 64 Views
  • Uploaded on

www.iupui.edu/~lab59. Interactions between lipid membranes. Horia I. Petrache. Department of Physics. Indiana University Purdue University Indianapolis, USA. Support:.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Interactions between lipid membranes' - velvet


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

www.iupui.edu/~lab59

Interactions between lipid membranes

Horia I. Petrache

Department of Physics

Indiana University Purdue University Indianapolis, USA

Support:

IUPUI Biomembrane Signature Center IUPUI Integrated Nanosystems Development Institute Alpha 1 Foundation NIH Generous student volunteering

slide2

You can contribute with:

  • More (better) theory
  • Applications
slide3

Lipid molecules have two parts

5- 7 Å

dipolar head

15- 25 Å

oily tails

slide4

Lipids aggregate and form bilayers (membranes)

~ 40 Å

Visible by X-ray depending on electron density.

slide5

Electron densities at T = 300 K

liquid water

lipid

Zero net density contrast but...

slide6

Electron densities at T = 300 K

lipid headgroup

lipid tails

compared to 0.333 e/Å3 for water

=> can see them!

slide8

X-ray scattering from oriented lipid membranes

Biophys. J. 2005,

J. Lipid Research, 2006

slide9

X-ray scattering from multilayers (1D randomly oriented lattice)

Scattered beam(s)

2q2

Bragg rings seen on the detector

Incident beam

2q1

MLV

sample

Bragg’s Law

slide10

Bragg’s Law

With D = 60 Å, l = 1.54 Å, and h = 1, obtain

(small angle)

q = 0.74o

=> Need a small x-ray machine

angle

slide11

detector

sample chamber

x-ray source

(tube)

slide12

Fixed anode BrukerNanostar U, 40 kV x 30 mA.

Wavelength = 1.54 Å (Cu source)

Sample-to-detector distances: 0.15 m, 0.6 m, and 1 m

Lattice spacings: 8 Å to 900 Å

slide13

Electron density of a typical lipid bilayer

0.333 e/Å3

Note: broad distributions (no sharp lipid-water interface)

slide14

Higher spatial resolution from oriented samples

(DLPC: a lipid we like)

J. Lipid Research 2006

slide15

Electron microscopy of lipids in water

Cryo-EM,

DganitDanino, Technion, Israel

slide16

Equilibrium distance means

attractive force + repulsive force = 0

F2

F1

D-spacing

=> Any measured change in distance means a change in membrane forces.

slide19

1 Molar = a pair of ions for each 55 water molecules.

100 mM = 10 times less ions or 10 times more water.

Debye screening lengths for electrostatic interactions in solution:

10 Å in 100 mM monovalent ions

3 Å in 1M

slide20

Example: D-spacing increases in KBr

DLPC/water

20mM KBr

40mM

60mM

80mM

100mM

200mM

400mM

600mM

q (Å-1)

slide21

Example: D-spacing increases in KBr

DLPC/water

20mM KBr

40mM

60mM

80mM

100mM

200mM

400mM

600mM

q (Å-1)

slide22

Equilibrium distances depend on polarizabilities (as expected)

.

Numbers indicate polarizability ratios

Szymanski, Petrache, J. Chem. Phys. 2011

slide23

...but need to explain a curiously large difference between

the effects of KBr and KCl

KBr

Water

spacing

KCl

slide25

Attractive interactions between lipid bilayers

van der Waals

With Hamakerparameter H ~ 1-2 kBT

Hamaker, Parsegian, Ninham, Weiss,...

slide26

Repulsion #1

(lipids don’t want to give water away)

hydration repulsion

Empirical exponential form with two adjustable parameters:

Ph~ 1000 – 3000 atm

l ~ 2 – 3 A

Rand, Parsegian, Marcelja, Ruckenstein, ...

slide27

Repulsion #2

(membranes bend and undulate)

shape fluctuation

KC=bending moduluss = fluctuation amplitude

Helfrich, de-Gennes, Caillé

slide28

Repulsion #3

(electric charges exist)

electrostatics: some analytical forms, mostly numerical calculations

Poisson-Boltzmann, Debye-Huckel, Gouy-Chapman, Andelman, ...

Main parameters:

membrane surface charge

Debye screening length (of the electrolyte)

slide29

Additivity/separability model of membrane interactions

+ elec

shape fluctuation

hydration

vdW

Fitting parameters: Ph, l, H, KC

Also need s(DW)

Parsegian, Nagle, Petrache

slide30

Long story short: s(DW)from X-ray line shape analysis

(DOPC and DOPS are two popular lipids)

Petrache et al., Phys. Rev. E 1998

slide31

Osmotic pressure

It can be measured with an osmometer.

slide32

Reduce inter-membrane spacing by using osmolytes

(e.g. polyethylene glycol, PEG)

Rand and Parsegian, 1979

PEG

Lipid

slide33

Example of interaction analysis giving Ph, l, H, KC

(no electrostatics)

hydration

fluctuations

vdW

Zero pressure

di(14:0)PC (DMPC) at 35oC

slide34

Practical method: use well calibrated reference lipid to investigate salt/electrolyte effects on membrane interactions

Main results:

Screening of vdW interactions

Electrostatic charging due to affinity of polarizable ions to lipids

Some interesting complications at the water/lipid interface

Koerner et al., Biophys. J. 2011

Danino et al. Biophys. J. 2009

Rostovtseva et al. Biophys. J. 2008

Petrache et al., PNAS 2006

Kimchi et al., J. Am. Chem. Soc. 2005

slide35

Fit with ~50% vdWreduction (no elec.)

Fluid

DLPC at 30oC

1M salts

water

KCl

KBr

Water spacing (Å)

J. Lipid Res. 2006

slide37

Obtain vdW strength (H) vs. salt concentration

Water

spacing

Br

Cl

Expect

(according to Ninham, Parsegian)

slide39

Detect electrostatic charging due to zwitterions

Koerner et al., Biophys. J. 2011

Common pH buffers

Our calibrated lipid

slide42

...and electrostatic charging

(at total 200 mM concentration)

slide43

Measure charging by competition with calibrated KBr

neutral point: 75% MOPS, 25% KBr

% MOPS replacing KBr

(at total 200 mM concentration)

slide46

Conclusions

[1]X-ray scattering measurements on well calibrated membrane systems provide experimental parameters for vdWand electrostatics. Experiments show larger screening length (reduced screening power of salt ions) than predicted theoretically.

[2] Can detect weak electrostatic interactions by competition measurements (e.g. MOPS vs. KBr).

[3] Water, mobile charges, and membrane fluctuations complicate calculations of interactions. Huge room for improvement.

slide47

Visit us at www.iupui.edu/~lab59

Acknowledgements

Megan KoernerZwitterions

Ryan LybargerBuffers, mixtures

Jason WalsmanE. coli (adaptation to ionic sol.)

Torri Roark Lithium salts

Johnnie Wright Exclusion measurements

Luis Palacio, Matt JusticeX-ray

slide48

Acknowledgements (cont.)

John Nagle (Carnegie Mellon Univ., USA)

Stephanie Tristram-Nagle (Carnegie Mellon Univ., USA)

Daniel Harries (Hebrew Univ., Israel)

Luc Belloni (Saclay, France)

Thomas Zemb (formerly at Saclay, France)

Adrian Parsegian (Univ. of Massachusetts, formerly at NIH)

Rudi Podgornik (University of Ljubljana, Slovenia)

Tanya Rostovtseva (NIH, USA)

Philip Gurnev (NIH, USA)