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33 Cards in this Set
- Front
- Back
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Orientation of multi path protein.
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Hydropathy profiles
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Hydropathy profiles
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Determine average hydropathy index for 5 amino acid window
Move window over one amino acid, determine again Plot hydropathy average vs. position of amino acid in polypeptide |
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Post-translational modifications in the ER.
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Newly made proteins in the ER membrane and lumen undergo modification
Disulfide bond formation Folding Glycosylation Assembly into multimeric proteins Only properly folded and assembled proteins pass through Golgi to final destination = “quality control” |
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Correct disulfide bond formation
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PDI= protein dissulfide isomerase
(formation of this facilitate through the process of reduction of oxidized PDI) |
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Rearrangement of disulphide bonds
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as a ways to
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Protein glycosylation in the ER
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Most plasma membrane and secreted proteins contain attched carbonhydrate chains ( N-linked, O-linked)
N-linked: a preformed oligosaccharide is added to Asn residues of many proteins in the ER, as they are synthesized. |
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Oligosaccharide: (Glc)3(Man)9(GlcNAc)2 formed
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on Dolichol phosphate, an ER phospholipid. First step in formation of Dolichol oligosaccharide inhibited by tunicamycin
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Oligosaccharide processed prior to passage to Golgi:
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quality control
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Added only at Asn residues flanked by
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X-Ser or X-Thr (C-side)
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The proteins is attached to
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the N-glucosamine on the terminal that linked to the proteins.
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Quality control:
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Obligosaccharide modification & chaperone proteins (Calnexin, Calreticulin)
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Chaperone binding provides
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time for proper folding by preventing unfolded proteins from exiting ER
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mannose removal
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export to Golgi
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Unfolded protein response
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Bip
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BiP
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Hsc 70 protein of ER lumen facilitate protein folding
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Unfolded protein
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bind to BiP, release BiP from Ire
Unbound Ire dimenrizes -> Activates endonuclease |
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Endonuclease cleaves Hac1 mRNA, allows production of Hac1 protein
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Hac1 enters nucleus, stimulates transcription of folding proteins
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Protein import into mitochondria and chloroblast
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Happen mostly post- translational !
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Un coupler prevents
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a proton gradient from happening
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Mitochondirial signal sequences
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Matrix, some inner membrane proteins have N-terminal signal sequence that is removed by peptidase
Outer membrane, some inner membrane: internal signal sequences Signal sequences necessary and sufficient for targeting Matrix signal sequences: amphipathic helix |
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Amphipathic helix
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The sequence has alpha helix. One side is hydrophoic the otehr is hydrophilic which recognize the signal
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Protein import into matrix
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chaperones and receptor
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Keeping the protein in its unfolded state is
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essential to allow its passage into the matrix
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Newly made protein associates with
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chaperone (Hsc70). Energy from ATP hydrolysis keeps protein unfolded.
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Targeting sequence associates with import receptor
Precursor transferred to |
Tom 40 import channel in outer membrane,
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Tom associates with
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Tim channel in inner membrane
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Protein drawn into matrix by proton motive force, associates
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with matrix Hsc70
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Targeting sequence cleaved, association
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with Hsc60 (some)
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Inner membrance
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Targeting ( null)
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Precursors have “bi-functional” presequence:
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matrix targeting + IMS targeting
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Precursor enters
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like matrix protein.
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Matrix targeting seq cleaved
IMS targeting seq stops in I.M. during import, dissociates from |
Tim channel, IMS targeting sequence cleaved
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Outer membrane: matrix targeting but
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“stop transfer” sequence anchors in outer membrane before transfer to matrix
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