Ch24_xray2

Ch24_xray2 - polar headgroup X-ray scattering/diffraction lectures Ch24 apolar tail membrane bilayer structure phospholipid S.J Singers fluid

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1 X-ray scattering/diffraction lectures Ch24 February 15, 2011 February 17, 2011 D.C. Rees 363 Broad [email protected] membrane bilayer structure S.J. Singer’s fluid mosaic model Science 175 , 720 (1972) apolar tail polar headgroup phospholipid phospholipids assemble into a bilayer through the “hydrophobic effect”; the apolar interior of the membrane is largely impermeable to water, ions and other polar molecules. Membrane proteins are required for transport of these species into and out of cells Molecular dynamics simulation of phospholipid bilayer = phosphate location 20 Å 40 Å Heller et al. J Phys. Chem. 97 , 8343 (1993), fbilayer.pdb z ˆ s o ˆ s ! S F ! S ( ) = 2 A " z ( ) # cos 2 $ Sz ( ) dz F(S) S F(S) S d S = h/d Scattering from membranes h=1 2 3 4 Y.K. Levine and M.H.F. Wilkins Nature New Biol. 230, 69 (19 6 5 4 3 2 1 0 -1 -2 -3 -4 -5 -6 Neutron and x-ray analysis of multilayers Wiener and White, Biophys. J. 61, 434 (199
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2 one bilayer stacked bilayers multilayers ! (e/Å 3 ) z (Å) the average density of a bilayer is < ! > ~ 0.32 e/Å 3 and for the hydrocarbon region is < ! > ~ 0.25 e/Å 3 electron density profiles of membranes Wiener and White, Biophys. J. 61, 434 (1992) Bernal, Nature 143 , 663-7 (1939) Protein Crystallography JACS 61 , 1860 (1939) Annual growth of macromolecular structures in the PDB as of February 8, 2011 61,841 x-ray 354 EM 8759 NMR 71,138 total (includes 184 “other” and “hybrid”) first high resolution protein structure published Feb 13, 1960 Why X-rays? carbon-carbon bond is about 1.54 Å (1.54 x 10 -10 m) X-ray wavelengths are of molecular dimensions (~10 -11 to 10 -8 m) Rhodes Crystal ography Made Crystal Clear Crystals are generated by translational repeats of a basic building block (the unit cell) and so contain many copies of the same unit held in a speci±c orientation (water-soluble) protein crystals contain ~50% solvent a crystal (0.1 mm) 3 contains about 0.7 μg protein (protein ! ~ 1.3 mg/mm 3 ) For M ~70 kD, this is about 0.01 nmole protein ~ 10 13 molecules ~ 10 mM protein in the crystal a crystal (0.01 mm) 3 =(10 μ) 3 contains about ~0.7 ng protein ~0.01 pmole ~10 10 molecules Why Crystals?
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3 crystallization want a slow approach to (super)saturation resulting in crystal formation (not precipitation)
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Ch24_xray2 - polar headgroup X-ray scattering/diffraction lectures Ch24 apolar tail membrane bilayer structure phospholipid S.J Singers fluid

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