D103 - Lecture 12 - Protein Sorting III.docx

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Biological Sciences
Grant Mac Gregor

A. Mitochondrial Import a. Everyone needs to go through TOM i. Must be unfolded b. Having a sorting signal i. Requires the membrane potential 1. Only affects proteins going into the mitochondrial matrix B. Clicker Questions a. How would this protein be inserted into the membrane (ER membrane) i. 1 sorting signal, 2 transmembrane domains ii. N-terminus in ER lumen, C-terminus in ER lumen b. Extra SRP proteins aren't required for more transmembrane domains c. Based on the first transmembrane domain B. Clicker2 a. Non-hydrolyzable GTP is added to a vesicle formation? i. Vesicle forms, but does not fuse ii. Fusion machinery is hidden by the coat 1. Coat will fall apart after the GTPase leaves a. GTP must be hydrolyzed B. Import into the ER occurs co-translationally a. Glycosylation also occurs co-translationally B. Events in the ER a. No disulfide bonds in the cytosol B. N-linked glycosylation a. Asn (N) b. Asn-X-Ser/Thr i. Consensus ii. Necessary but not sufficient b. Glycosylated at the Asn c. Dolichol i. Longer lipid ii. Covers both leaflets of the rough ER iii. Holds onto the sugar three (glycol) b. Occurs co-translationally c. Used for i. Quality control ii. Lysosome sorting signal M6P B. Quality control in the ER a. Glucosidase i. Removes terminal glucoses b. Asn i. Has a sugar tree with 3 glucose at the end b. Lectin i. More specfically- Calnexin ii. Chaperone (membrane bound) iii. Recognizes the sugar tree with one glucose 1. Then binds and folds the protein ii. Last glucose is removed by a glucosidase iii. Normally the protein is released from Calnexin 1. To allow it to leave the ER b. Glucosyltransferase i. Can reglycosidate to tell the protein to refold again B. UnFolded Proteins response a. Chaperone i. Calnexin, BiP 1. Irreversibily binds to misfolded proteins 2. Increases the transcription of chaperones and folding catalyst b. Retrotranslocated back into the cytosol i. Ubiquitin will bind to the misfolded protein 1. At lysines ii. Proteasome degrades poly-ubiquitinated proteins B. Cystic fibrosis a. Characterized by thick mucus buildup b. Disregulation of water metabolism c. CFTR i. Ligand-gated 1. ATP-gated ii. Chloride channel 1. Chloride will move out
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