L8 - Proteolysis 2

Question 1

compare and contrast lysosomnal and ubiquitin-proteasome pathway

Answer 1

lysosomal pathway:
- membrane-bound lysosome
- proteins,organelles , extracellular material
- triggered by autophagy signals,nutrient starvation
- low specificity
- low energy requirement –> acif hydrolases
- storage diseases –> I-cel

Ubiquitin-proteosome:
- cytosolic 26S proteosome
- specific intracellular proteins
- ubiquitin signals/tags
- high selectivity -> protein specific
- high energy requirement -> ATP-dependnat unfolding + transaction
- cancer,neurodegeneration

Question 2

why is ubiquitin descrived as molecular barcode

Answer 2

attached to proteins in different topologies - mono,multi or poly

= polyubiquitin chains canbbe linked togther by different lysine residues each converying a different cellular message

= this specific ubiquitin ‘code’ determines fate of tagged protein –> barcode scanned by ‘readers’

Question 3

what do the polyubiqutin chains on lysines K48 and K63 target for

Answer 3

K48 linkage - signals for porteosomal degredation

K63 - signalling,DNA repair,endocytosis

Question 4

what do isopeptide bonds form between in ubiqutin and lysine on target protein

Answer 4

C-terminal glycine of ubiquitin + ε-amino group of a lysine residue on the substrate

Question 5

why are isopeptide bonds between ubiquitin and lysine on substrate important

Answer 5

stable anjd specific –> allows precise attachment of ubiquitin

creates code for different ecllular outcomes

Question 6

role of E1,E2 and E3 enzymes in atgging substartes with ubiquitin

Answer 6

E1 - ubiquitin activating:
activates ubiquitin using ATP = forms Ub-E1 thioester bond

E2 - ubiqitin-conjugating:
receieves Ub from E1 –> forms Ub-E2 complex

E3 - ubiquitin ligase;
transfers ubiquitin from E2 too substrate lysine

Question 7

why are there so many E3 ubqiuitin ligase genes

Answer 7

allows cells to slectively target vast array of proteins for ubiqiutination

= ensures tigfht regulation of protein turiover and quality

Question 8

whar molcular signs are ther for ubiquitin

Answer 8

phosphorylation

N-terminal residue identity = N-end rule

misfolded or unassembled proteins

Question 9

what is the N-end rule

Answer 9

The N-terminal residuye actsas a degredation signal

= depdning what amino acid is present at posiyion 1 changes whether protein is:
- stable
- unstabe = degraded by proteosome

Question 10

describe the structure of proteosome

Answer 10

26S proteasome = 20S core particle (CP) + 19S regulatory particles (RPs)

20S CP = cylindircal containging β subunit with proteolytic active sites

19S RP = recognises polyubiquitinated proteins -> unfolds them -> threads them through core

Question 11

describe the function of proteasome

Answer 11

recognises K48-linked polyuniquitin chains

removes ubiquitin before degredation

degrades substrate into small peptides by β subunits of 20S CP

Question 12

what ahppens to the small peptides produced by proteasome

Answer 12

further broken down by cytosolic peptidases into amino acids

recycled for :
- new protein synthesis
- energy

uniquitin recycled by deubiquitinating enzymes

Question 13

what does parkisnosn have a defect/mutation in

Answer 13

E3 ubiquitin ligase

= acumalation of damaged proteins