The Fluid Mosaic Model

Singer & Nicholson, 1972

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Lipid Protein Ratios

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Protein Lipid

Axon 75 25

Mitochondrial outer 20 80

Mitochondrial inner 75 25

Plasma 50

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Basic Membrane Structure

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Membrane Components

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Cardiolipin

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Membrane Compositions

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P-Lipid G-Lipid Chol PE PC PG PI PS PA S CL GD SM

Erythrocytes

24 - 9.2 30.2 24.5 - 3 15.1 - - - - 27.2

Myelin 33 22 17 14 11 - - 7 - - - - 6

Microsomes 25 4 7.5

Rod outer 27 9.2 2 30 27.5 - 2 7 - - - - 2

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Structure of the Bilayer

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Langmuir Trough

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Molecular Area

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15

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Dynamics of The Bilayer

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Dynamic Timescales

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Motion Time Scale -log(s)

Bond vibration -14 to -13

Proton transfer -12

Hydrogen bonding -12 to -11

Rotation of side chains at surface -11 to -10

Helix breakdown/formation -8 to -7

Allosteric transitions -5 to 0

Rotation of sidechains -4 to 0

Lateral Diffusion (1mm) -1 to 0

Lipid Flip Flop (uncatalyzed) 3 to 4

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DSC and phase transitions

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Isolation of Membrane Proteins

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Micelle Formation

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Micelle Formation

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Lipid/detergent Bicless

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Patch Method

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Detergents and Bicelles

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Membrane Proteins

• Membrane proteins account for 25-35% of genome in living organisms.

• There are over >45,000 structures of water-soluble proteins,

• but only ~150 unique structures of membrane proteins.

• Membrane proteins account for ~50% of all therapeutic targets

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Functions

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Definitions

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Type ONE Outside N-tErminus

Membrane Protein Topologies

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Historical Milestones in Membrane Protein

Structure Determination

• 1977 Bacteriorhodopsin (EM), Henderson and Unwin, Nature

• 1984 Photosynthetic reaction center, Deisenhofer et al, JMB

• 1990 Bacteriorhodopsin, Henderson et al, JMB

• 1992 Porin (beta-barrel), Weiss & Schulz, JMB

• 1998 K+ channel, Doyle et al, Science

• 2000 Rhodopsin, Palczewski et al, Nature

• 2007 GPCR, Rasmussen et al, Nature

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Helical Protein: ATP/ADP Carrier

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Beta Barrel: OmpG

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The Beta Sheet

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Hydropathy

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Hydropathy Analysis • http://blanco.biomol.uci.edu/mpex/

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Positive Inside Rule

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Close in Sequence

Close in Space

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N - Term

C - Term

Gene Duplications • Many helical membrane proteins (~60%) contain homologous domains with

opposite membrane orientation.

• Pseudosymmetry

• Example: Aquaporin 1

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Protein Folding

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Conformational Energetics of Rhodopsin Modulated by Nonlamellar-Forming Lipids†

Ana Vitória Botelho,‡, Nicholas J. Gibson,§, Robin L. Thurmond,‖,, Yin Wang,#, and, and

Michael F. Brown*,‡,‖ Biochemistry 2002 41 (20), 6354-6368

Membrane Protein Folding

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Sec61/SecY

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Insertion of TM Helix

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Sec61/SecY Channel

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E. Coli PCC/Ribosome

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Membrane Receptors

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TCR/CD3 Receptor

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GPCR Signalling

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GPCRs

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GPCR Signalling Schema

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