Lect3_ProteinSort

Lect3_ProteinSort - Types of cellular localization signals...

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Types of cellular localization signals 1. Signal sequence -short sequence of aa -signal sequence can be within the protein or at the terminal ends of the protein 2. Signal patch -made up of amino acid residues that are distant to one another in the primary sequence, but come close to each other in the tertiary structure of the folded protein 3. Specific sugar molecules can act as a localization signal 1 Cell Biology – lecture 2 © Gross - all rights reserved.
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Each destination in the cell requires the correct sorting signal (ticket!) Signal-mediated protein transport to: 1. mitochondria 2. nucleus 3. ER: the starting point of the secretory pathway (Golgi, vesicles, PM, ECM) 4. Lipid droplets Amino acid key: Yellow = hydrophobic Pink = + charged aa Blue = - charged aa Yellow 1 2 3 2 Cell Biology – lecture 2 © Gross - all rights reserved.
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3 necessary : it should direct a protein into a new, membrane- enclosed compartment, or attach it to an organelles surface -->results in the protein’s protection from proteases sufficient : it should direct a neutral protein (without sorting information) to the new environment • It should specifically interact with a binding partner/receptor • It can be removed from the protein upon arrival in target location What is expected of a sorting signal? Cell Biology – lecture 2 © Gross - all rights reserved.
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Considerations for transport of a protein to its destined location 1. Protein to be transported has to have a sorting signal - necessary to direct the protein to the new location - should be sufficient to direct any random protein to that location 2. Sorting signal typically recognized by a specific receptor 3. Receptor should bring the protein to a translocation machinery site (if brought inside) 5. Release of transported protein into the new environment 4. The protein should be kept in a translocation competent state 4 7. Folding/processing into native configuration completed 6. Driving force for transport ( energy source?) Cell Biology – lecture 2 © Gross - all rights reserved.
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Case 1: Protein import to Mitochondria 5 Basic concepts of trans-membrane protein delivery: 1. Recognition, 2. Insertion, 3. Translocation, 4. Cleavage Cell Biology – lecture 2 © Gross - all rights reserved.
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The destinations in mitochondria 1. Matrix (enzymes of the Citric Acid cycle) 2. Inner membrane (respiratiory chain complexes) 3. Intermembrane space (cytochrome c) 4. Outer mito membrane (porin) 6 Cell Biology – lecture 2 © Gross - all rights reserved.
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Mitochondrial protein import ( matrix) 1. Mito precursor proteins are synthesized in cytosol, kept in unfolded state by chaperones (Hsc 70) 2. Import receptor recognizes matrix- targeting sequence 3. Receptor transfers protein to the general import pore (Tom 40) 4, 5. Protein translocates through outer (Tom 40) and inner (Tim 44) membrane channels. Matrix chaperone (Hsc 70) binds protein as it enters to prevent premature folding 6. Target sequence cleaved 7. Chaperone proteins removed, protein folds and becomes active Mitochondrial import requires receptors and translocons: Tom
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This note was uploaded on 12/13/2011 for the course BIOSCI d103 taught by Professor Staff during the Fall '11 term at UC Irvine.

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Lect3_ProteinSort - Types of cellular localization signals...

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