In strands within a barrel successive amino acids

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Unformatted text preview: ­strand Whole Bilayer ≈40 Å ≈11 ­12 residues Hydrocarbon Core ≈30 Å ≈9 residues β ­barrel membrane proteins Structures: closed β ­sheets, called β ­barrels. Forms channels in the membrane •  in most β ­barrels the strands are not oriented perpendicular to the membrane so more than 9 residues are typically required to span it. •  β ­sheets need to span, can’t stop in the middle. Why? Porin •  Porin forms a hydrophilic pore to allow sugars or other polar metabolites to cross the membrane. •  DistribuEon of hydrophilic and hydrophobic residues in the β barrel membrane protein porin. hydrophilic residues Higher ConcentraWon Membrane Lower ConcentraWon hydrophobic residues Topology of Porin •  up ­down ­up ­down pa_ern in which each successive β ­strand is spaEally adjacent to the one that precedes it in the sequence. •  In β ­strands within a barrel, successive amino acids alternately point into the barrel interior and outward from the exterior. The barrel interior is somewhat polar, prevenEng long runs of hydrophobic residues. Hydropathy plot for porin ? Hydropathy plot for porin ? A hydropathy plot for porin does not reveal any obvious transmembrane regions. In general, it is more difficult to determine the topology of β ­ barrel membrane proteins from the sequence. DistribuEon of amino acids in membrane proteins Color scheme: Tyr Trp Lys, Arg, Glu, Asp LocaEon of charged residues ? Why Tyr, Trp are located at the boundary? Examples of membrane β ­barrels and their funcEons Lysis of cells Iron transport Phospholipase (lipid metabolism) (offense) Sugar transport Some (but not all) allow passage or transport of molecules a...
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This test prep was uploaded on 02/25/2014 for the course BIOC 462A taught by Professor Ziegler,baldwin during the Spring '08 term at University of Arizona- Tucson.

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