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BCHE 395-16 2014 Membranes and Transport I

Integral membrane protein bacteriorhodopsin 7 segment

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Unformatted text preview: acids would be associated with hydrophobic and hydrophilic regions •  Integral Membrane Proteins –  Have hydrophobic domains –  Very firmly bound to lipid bilayer, “buried” –  “SolubilizaFon” requires harsh detergent •  Amphoteric –  In cytosol and associated with membranes –  Generally have regulated, reversible associaFon •  Peripheral –  Loosely bound, or parFally buried (H- bonds, electrostaFc) –  Released by high salt –  Not very hydrophobic NOTE the different measures used to release membrane proteins Integral Membrane Proteins •  Can rapidly move laterally in the membrane •  Do NOT rotate in the membrane •  Contain a high proporFon of hydrophobic amino acids in the regions that are embedded in the membrane •  Segments that span the membrane are ooen (but not always) α- helical and β- barrels •  Have asymmetry like the membrane –  Different domains in different compartments Integral Membrane Protein •  Glycophorin •  In red blood cells •  Carbohydrates O- linked to S, T •  All CHO modified amino acids on outside ( ) •  Transmembrane α- helix: about 20 residues, mostly hydrophobic •  Review what occurs when treat with trypsin! Integral Membrane Protein •  Bacteriorhodopsin •  7- segment “serpenFne” moFf –  α- helices –  Common in signal recep8on proteins –  See this structure in Adrenergic receptor, Yeast maFng factor receptor Light- driven proton pump PredicFng Transmembrane Helices •  Hydrophobicity plotsà༎ Assign “index of hydrophobicity” to each amino acid (measures free energy of transfer to water) 20- 25 aa stretch can •  Scan AA sequence for regions of high span a membrane hydrophobicity Glycophorin Fig. 11- 11 Bacteriorhodopsin Amino acids in membrane proteins cluster in disFnct regions •  Transmembrane segments are predominantly hydrophobic •  Tyr and Trp cluster at nonpolar/polar interface •  Charge...
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