W12L1 post translational regulation

Question 1

Method of post translational regulatory

Answer 1

1. Protein folding
2. The ubiquitin proteasome system
   3.autophagy

Question 2

Proteostasis in eukaryote

Answer 2

The process of controlling proteins abundant, consist of
-protein synthesis
- protein maturation via protein folding and post translational modification
- when it is no longer required , degradation occur

Question 3

Post-translational events

Answer 3

-Several steps are required to produce a functional protein
-The first step is protein folding
- covalent modification
- binding to other subunit
- maturation of functional protein

Question 4

Protein folding

Answer 4

• polar and non polar side chains
  -polar side chain on the outside of the molecule can form hydrogen bonds to water
  -hydrophobic core region contains nonpolar side chain
  -Hydrophobic residues move towards the centre of the protein

Question 5

Protein folding begins during translation

Answer 5

Some proteins can fold by the time synthesis is complete But most cannot fold correctly without help

Question 6

Discovery of heat shock proteins

Answer 6

Heat-shock proteins (Hsp) are molecular chaperones
Rapidly induced by mild heat shock
Are conserved in bacteria, plant, animals

Question 7

Molecular chaperones assist with protein folding

Answer 7

-Hsp70 binds to hydrophobic regions of unfolded proteins
-Rapid cycles of ATP hydrolysis induce conformational changes and dissociation/association of Hsp70 to assist folding
-Hsp60 provides an isolated environment for protein folding forcing the incorrectly or incompletely folded protein to fold correctly. high amount of hydrophobic residue
- have hydrophobic binding site to attract, ATP cause GroES cap to bind
- GroES cap force the hydrophobic region to be inside and the hydrophilic out

Question 8

Reason for Proteins cannot always be successfully folded

Answer 8

• mutation
• incorrect splicing
• cell stress
• overexpression
• bad luck

Question 9

The Ubiquitin Proteasome System (UPS)

Answer 9

Proteins are targeted to proteasome for degradation and recycling By the 26S proteosome

Question 10

Ubiquitination process of poteins

Answer 10

-Ubiquitin is added to lysine residues in proteins
-poly ubiquitination of Lys48 target the protein to proteosome
-Poly-ubiquitinated proteins are degraded by the 26S proteasome

Question 11

Ubiquitin Ligases

Answer 11

3 type:
E1 is ubiquitin activating enzyme, using ATP
E2 receive ubiquitin from the E1
E3 ligases interact with the E2 and the protein substrate
E2 then transfer ubiquitin to the substrate

In humans, 2 E1 enzymes, ~30 E2 enzymes, >500 E3 proteins

Question 12

Diversity of E3 ubiquitin ligases

Answer 12

Cullin-RING-ligase (CRL) type
Non CRL type

Question 13

The unfolded protein ubiquitin response

Answer 13

Misfolded proteins in the ER are targeted to the proteasome
-ubiquitine ligase presented on the ER membrane
Ubiquitinated by an E3 ligase as they are exported from the ER

Question 14

The unfolded protein response and translational repression

Answer 14

-PERK detects unfolded proteins in ER by detecting the hydrophobic region
-PERK is eIF2⍺ kinase, a global repressor of translational initiation
-phosphorylation of eIF2⍺ leads to Increase of ATF4 translation due to uORFs

Question 15

Median of protein life

Answer 15

46 hours
Regulated protein degradation occurs by the UPS

Question 16

Skp, Cullin, F-box (SCF) family of ubiquitin ligases

Answer 16

F-box proteins define specificity of the SCF complex: 69 in humans, ~700 in Arabidopsis

Question 17

Fbox and phytohormomes

Answer 17

-F-box proteins are receptors for phytohormones
-When there are low levels of hormone in the cell Transcriptional repressors inhibit hormone-response genes
-Hormones bind to the F-box protein to recruit repressor proteins
-Degradation of repressor proteins by UPS activates transcription
-The F-box protein creates substrate specificity

Question 18

What is autophagy

Answer 18

Autophagy mean self death, a mean to recycle cell component
Conserved pathway in fungi, plant and animal

Question 19

Process of autophagy

Answer 19

Autophagy directs material to the lysosome or vacuole
-create a membrane around the target, a membrane bound organelle target it for degradation
- The lysosome is an acidic compartment containing enzymes for degradation

Question 20

Genetic screen for autophagy mutants

Answer 20

Autophagy first described in 1960s, but no molecular understanding until 1990s . Very difficult to observe in vivo, needing electron microscope
- generate vacuolar proteinase mutant, Autophagic bodies accumulate in vacuoles under nutrient stress, visible with a light microscope

Question 21

Initiation and formation of autophagasomes

Answer 21

• Tor also regulate autophagasome synthesis
• active Tor also phosphorylation Atg13 to inhibit autophagy
  -Under starvation mTORC1 is inactive, Atg13 promotes autophagy

Question 22

A ubiquitin-like conjugation system

Answer 22

Atg12 and Atg8/LC3 ubiquitin-like proteins, can covalently link to a peptide
-Atg 7 is an E1 like, bind to Atg 12 and Atg8
-then transfer to E2 like protein Atg10 and Atg3
-ultimately, Atg8 and Atg12 conjurgate to PE
Phosphatidylethanolamine (PE) is a membrane phospholipid
> Required to form autophagasomes