Intracellular proteolysis
Terms
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- What are the major pathways for degredation?
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1. autophagy (macroautophagy, microautophagy, direct protein transfer) LYSOMAL DEPENDENT PATHWAYS
2. 26S Proteasomes and the ubiquitin dependent pathway. - what is autophagy?
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the break down of cellular materials (usually dependent on lysosomes)
-involved in the intracellular destruction of endogenous proteins and the removal of damaged organelles
-necessary for cell homeostasis and cell remodeling during differentiation, metamorphasis, non-apoptotic cell death, and aging.
-very highly regulated
-the main means of degradation for long lived proteins and the only means of turn over for membrane organelles like mitochondria and peroxosomes - -the main means of degradation for long lived proteins and the only means of turn over for membrane organelles like mitochondria and peroxosomes
- autophagy
- macroautophagy
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part of the ER forms a double membrane vesicle, that consequently fuses with a lysosome
- the inner membrane of the autophagosome along with the protein and organelle contents are then degraded by lysosomal proteases and then the products are all recycled - examples of proteins that are degraded by chaperone mediated autophagy
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-glycolytic enzymes
-transcription factors
-transcription factor inhibitors
-subunits of some cytostolic proteases - KFERQ
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a signal that means I am a protein that should be degraded by chaperone mediated autophagy
-motif recognized by a chaperone, the chaperone binds the protein and binds the lysosomal membrane through protines and then the protein is transfered into the lysomal matrix for degradation - hsc73
- chaperone protein that recognizes KFERQ signals in proteins that need to be degraded by chaperone-mediated autophagy.
- What are the units and full units of a proteasome
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caps are each 19s
the middle is 20s
total they are called a 26s - DUB
- deubiquitinating enzymes - recycles the ubiquitin so that it can be reused
- A key difference between lysome degradation (autophagy) and ubiquitin proteasome pathways - not obvious
- proteins degraded in a proteasome are still free in the cytoplasm or the nucleoplasm, whereas proteins degraded IN lysosomes had to cross a membrane
- Steps in the Ubiquitin proteasome pathway
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1. substrate tagging by covalent attachment of multiple ubiquitin molecules
2. degradation of the tagged protein by the 26s proteasome complex with the release of free and reusable ubiquitin. - 20s proteasome
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1. a multicatalytic macromolecular complex
2. subunits have trypsin, chymotrypsin, peptidyl-glutamyl hydrolyzing activites and an isopeptidase
3. has intrinsic proteolytic activity that is ATP dependent
4. ATP is required for degradation of ubiquitinated proteins - what protein residue are ubiquitin trees attached to?
- - lysine
- The Ubiquitinylation multistep process?
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1. Ub is activated by the enzyme E1 requires ATP
2. E2 (Ub conjugating enzyme) transfes Ub from E1 to the substrate that is already bound to E3 (ub-protein ligase)
- an isopeptide bond is formed between Ub and e-NH2 (Lysine) in the substrate protein
-a ubiquitin tree is formed by the transfer of Ub to previously bound Ub - E3
- Ub protein ligase
- E2
- Ub conjugating enzyme
- N end rule
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proteins with arg lys phe leu trp at the n terminal end are short lived
proteins with Cys, ala, ser, thr, gly, val or met at the N terminal end are long lived - Arg -X-X-Leu-gly-x-ile-gly-asx
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-near the n terminus
-targets them for destruction by UB mediated pathway
-caleld the destruction box - PEST sequence
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-targeted for Ub mediated degradation
-proteins with internal sequences enriched in Pro, glutamic acid, ser, thr - Proteins that are degraded by a ubiquitin mediated pathway
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-N end rule
-argxxleuglyxileglyasx
-PEST sequence