lecture0303final - Membrane proteins Integral membrane...

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Membrane proteins Integral membrane proteins. A hydrophobic section of the protein is  imbedded in the hydrophobic core of the lipid  bilayer – held there by the hydrophobic effect  Often extend all the way through the lipid  bilayer -  transmembrane proteins Peripheral membrane proteins Located outside lipid bilayer- held to polar  surface of membrane by weak bonds  Lipid anchored proteins Located outside bilayer but are covalently  bound to lipids that are part of the bilayer  structure
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Figure 4.12
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Integral membrane proteins – methods  for studying structure Crystals of membrane proteins  which retain their native  conformation are difficult to obtain,  so only a relatively small number of  definitive tertiary structures are  available via X-ray crystallography So a series of alternative methods  have been used to examine  membrane protein structure.
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Methods for studying integral membrane  protein structure 1) Freeze fracture electron  microscopy Can resolve gross dimensions of  membrane proteins, their density in the  membrane and whether subunit  (quaternary) structure exists. Cannot  resolve details of tertiary structure.
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Freeze fracture e. m. 
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Methods for studying integral membrane  protein structure 2) Extracting integral proteins from  membranes using nonionic  detergents allows later SDS gel  electrophoresis (determination of  MW), mass spectroscopy etc.  Triton X-100 – substitutes for  phospholipids  - surrounds the protein  and draws the protein out of the  membrane and into solution   
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lecture0303final - Membrane proteins Integral membrane...

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