Lysosomal Enzyme Pathway, Targeting, Mitochondria, and Chloroplasts

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  1. Lysosomal Enzyme Pathway (1 and 2)
    • (1)    made on ER ribosomesà taken to Golgi complex, where a phosphate group is added to the mannose sugars of the N-linked carbohydrate chains
    • (2)    the lysosomal enzymes are recognized and captured by a mannose-6-phosphate receptors, which recognize their mannose-6-phosphate signal
  2. Lysosomal Enzyme Pathway (3 and 4)
    • (1)    transported from the TGN in clathrin-coated vesicles, escorted by a family of adaptor proteins called GGAs, which bidn to clathrin on the outer surface
    • (2)    on the inner surface, the GGA adaptors bidn to a sorting signal in the cytosolic tails of the mannose-6-phosphate receptors, which then bind to a soluble enzyme in the vesicle lumen
    • a.       this causes concentration of both lysosomal enzymes and MPRs in the clathrin coated vesicles
  3. Lysosomal Enzyme Pathway (5 and 6)
    • (1)    Arf1 causes formation of the clathrin-coated vesicleà coat is lost and the vesicle proceeds to its destination
    • (2)    before reaching destination, MPRs dissociate from the lysosomal enzymes
  4. Targeting to particular places 
    • (1)    movement toward the specific compartment
    • (2)    tethering vesicles to the particular compartment
    • a.       rod-shaped, fibrillar and  large, multiprotein complexes of them
    • (3)    docking vesicles
    • (4)    fusion
  5. Mitochondria steps 
    • o   presentation in unfolded state
    • o   binding to chaperones, which prepare it for uptake
    • o   goes through TOM complex on the OMM
    • o   if going to the IMM or matrix, it must go through the intermembrane space and engage a second protein-import complex located in the IMM, called the TIM complex
  6. Mitochondria steps 
    • o   translocation occurs at sites where the outer and inner mitochondrial membranes come into close proximity
    • o   movement powered by proton-motive force
  7. Mitochondria steps 
    • o   as it enters the matrix, it interacts with molecular chaperones that mediate movement into the matrix, by either acting as force-generating motors to pull the unfolded polypeptide through the pore or aiding in the diffusion of the polypeptide across the membrane
    • if the unfolded polypeptide entered the translocation pore in the mitochondrial memrbaen and poked its head into the matrix, the chaperone would bind and block its causing further travel into the matrix
  8. Mitochondria steps 
    • o   in the matrix, chaperones bind to prevent diffusion backward (biased diffusion)
    • o   once in the matrix, the polypeptide achieves its native conformation following enzymatic removal of the presequence
  9. Chloroplasts
    Step 1
    • -          contain a transit peptide that provides an address, saying which subcompartment it will go in
    • o   all proteins translocated through the chloroplast envelope contain a stroma targeting domain as part of their transit peptide, which guarantees that the polypeptide will enter the stroma
    • o   this signal is then removed
  10. Chloroplasts
    Step 2
    -          those polypeptides destined to thylakoids also have a thylakoid transfer domain, which allow insertion into either the membrane or into the lumen
Card Set:
Lysosomal Enzyme Pathway, Targeting, Mitochondria, and Chloroplasts
2013-11-11 04:07:09
Cell Bio

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