Lecture 16- Removing and recycling cellular components by autophagy

Question 1

initial genes discovered to be important in autophagy

Answer 1

ATG genes in yeast

Question 2

purpose of autophagy

Answer 2

bulk removal of material, preventing cytotoxicity, removing unnecessary material

Question 3

what is TOR and its role

Answer 3

TOR (target of rapamycin) is a kinase which acts as the ‘master regulator’ of cell growth
specifically acts on ATG apparatus to prevent autophagy, and regulates the 26S proteasome

Question 4

mechanism of how TOR regulates autphagy

Answer 4

phosphorylates ATG13, which prevents ATG1 complex assembly
TOR is then inactivated under stress conditions, which then allows the complex to for

Question 5

steps of autophagy within the cytoplasm

Answer 5

-isolation membrane/phagophore forms
-isolation membrane expands and becomes spherical
-double membrane bound structure forms, known as the autophagosome
-transport of this to the lytic organelle, such as the lysosome
-degradation of material

Question 6

2 important autophagy systems

Answer 6

ATG8 and ATG12 systems

Question 7

ATG8

Answer 7

facilitates membrane expansion by allowing lipidation to occur

Question 8

ATG12

Answer 8

forms a conjugate with ATG5, which facilitates conjugation of ATG8 to the lipid, so is important in the lipidation process

Question 9

how can adding lipids aid in the production of an isolation membrane

Answer 9

thins out the membrane, adding 1 lipid at a time- curvature can cause instability which results in an overall curved structure of the membrane

Question 10

ATG8-PE- what is it, what does it do, where is it located

Answer 10

end point of isolation membrane formation

allows tethering and fusion of membrane-supplying vesicles
recruits other proteins to the isolation membrane
transport to, and fusion with, other vesicles such as the lysosomes

exists on the outside of the isolation membrane

Question 11

how does pore closure occur

Answer 11

membrane fission rather than fusion, using ESCRT machinery

Question 12

how selective is autophagy

Answer 12

not usually when it is due to nutrient deprivation- but can be selective, breaking down specific materials where this is necessary- e.g. dysfunctional or excessive organelles

Question 13

how can selective autophagy be triggered

Answer 13

due to stress signals, and autophagy receptors as a trigger- these can directly recruit ATG machinery to bypass the need for a TOR trigger

Question 14

example of an autophagy receptor

Answer 14

ATG8-interaction motif (AIM)- can bind AGT8
can become exposed on stress or become activated by phosphorylation

Question 15

how can Ub tagging lead to autophagy

Answer 15

cargo recognised by receptors, binding through AIM to AGT8, cargo becoming sequestered in the autophagosome for degradation

Question 16

mechanism of mitophagy

Answer 16

inhibition of TOM, a protein which usually deactivates parkin
depolarisation upon mt damage- leads to TOM inhibition
inhibition of PINK1 import, stabilisation at the MOM
parkin becomes active
eventual Ub coating and recognition, leading to breakdown

Question 17

examples of other forms of specific phagy

Answer 17

xenophagy- pathogen degradation
chlorophagy- happens in response to starvation

Question 18

what is microautophagy

Answer 18

autophagy which does not involve an autophagosome- but shaees some similar ATG apparatus

Question 19

example of how autophagy can be important in health and disease

Answer 19

accumulation of misfolded proteins has been associated with neurodegenerative diseases, and therefore a lowered ability to remove these aggregates may contribute to the development of the disease