3. mila Flashcards
Through which route are most ECM and plasma membrane proteins degraded?
- lysosomal pathway
Through which route are most cytosolic proteins degraded?
- ubiquitin-proteasome pathway
Through which route are most nuclear proteins degraded?
- ubiquitin-proteasome pathway
What types of proteins typically have a long t1/2? Why?
- collagens, structural proteins (~1yr) - myosin and actin in muscles (~1wk)
What types of proteins typically have a short t1/2? Why?
- enzymes that control metabolic pathways (minutes) e.g. Ornithine decarboxlyase at 11 minutes is used to catalyse commited step in polyamine production from ornithine (end product or urea cycle) - liver enzymes (~1day)
In what form do proteins enter the lysosomes? In what form do they exit?
- enter as… - exit as dipeptides and amino acids
What process precedes degradation by the 26S proteasome?
-Ubiquination - ATP-dependent conjugation of the protein target to multiple copies of ubiquitin
What is the function of oligopeptidases and why are these important?
- they degrade peptide products to dipeptides and free amino acids after initial attack of endopeptidases
What different reasons could there be for degradation of an endogenous protein?
- regularoty cellular proteins - damaged, misfolded or mutated proteins - most of the normal, long lived proteins
What is the difference between the proteolysis of digested proteins and the degradation of endogenous proteins?
- Higher levels of control -
Through which mechanism is material taken up by endocytosis degraded?
- lysosomal degradation
What is the difference between macro- and microautophagy and what organelle/s is/are involved?
- Macroautophagy - target engulfed in double membrane vesicle (autophagosome - form from small precursors) and outer membrane of vesicle fuses with lysosome (autolysosome) - Microautophagy - cytoplasm engulfed directly via invagination, protrusion - Organelles that are damaged are engulfed. Organelle that destroys is the lysosome
What similarities can you see between receptor-mediated endocytosis and chaperone-mediated autophagy?
- Target molecule must contain right structure/sequence to be recognised by receptors - Both involve movement of a molecule across a membrane
What differences can you see between receptor-mediated endocytosis and chaperone-mediated autophagy?
- CMA involves translocation across membrance, RME involves budding of vesicle -
What catalytic groups are represented amongst the lysosomal proteases?
- Cysteine proteases (e.g. Cathespsin B and C) - Aspartic proteases (e.g. Cathepsin D) - Serine proteases (e.g. Tripeptidyl peptidase I)
What is the #1 environmental condition required for lysosomal protease activity and how is this accomplished?
- low pH - Acidified via V-type proton ATPase which uses free energy from ATP hydrolysis to drive protons into the lysosome against concentration gradient
What is ubiquitin and what is its function in protein degradation?
- It is a small (76aa) protein that attaches to proteins to label for 26S proteasomal degradation - Highly conserved sequence, present in all eukaryotic cells - At least 4 ubiquitin must attach to signal degradation
Why do most substrates need to be unfolded prior to proteasomal degradation?
- Due to 13A width of inner chamber of proteasome, requiring at least partial unfolding to fit. 19S particle plays a role in the unfolding
What are the main differences between lysosomal and proteasomal degradation in terms of 1) pH optimum, 2) Catalytic class, 3) Energy requirement?
How can proteins enter the lysosome?
- endocytosis - microautophagy - macroautophagy - chaperone-mediated autophagy
What is a degron?
A degradation signal
