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trafficking and glycosylation 110209

trafficking and glycosylation 110209 - Trafficking and...

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Trafficking and Glycosylation - the Secretory Pathway as a Paradigm November 2, 2009 1. Protein translocation 1. Why? Cells must localize proteins to specific organelles and membranes Cytosol membranes 2. Types of membranes Rough ER Golgi Cell membrane Mitochondrial Peroxisomes Secretory vesicles Etc. 3. Endoplasmic reticulum and Golgi as gateways to secretion/endocytosis If these things are defective, you don’t make it, so they’re extremely important System of sheets and tubules Entry point for proteins into the secretory pathway Signal sequences target nascent secretory and membrane proteins to the ER for translocation (embedded into the membrane) o Clipped off once they’ve done their job o Very easily characterized Short stretch of amino acids that is hydrophobic, usually at amino terminus very Proteins cross the ER membrane through aqueous channel that is gated Secretory proteins: translocate completely across the ER membrane Transmembrane proteins are integrated into the membrane 4. Early 70’s Found signal sequence that localizes the protein to the membrane 5. SRP protein: RNA molecule with a couple of polypeptides at either end Recognizes the signal sequence as it exits the ribosome Slows the translation of the nascent protein Allows the ribosome to find the ER before it finishes translating Most translocational events are co-translational
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