Lecture 17: Cell death

Question 1

Structure and domain of caspases

Answer 1

3 domains
N terminal pro domain
central large subunit
small C-terminal subunit

have substrate specificity for aspartic acid residue at cleavage site
all have similar amino acid sequence and structure

Question 2

Zymogens

Answer 2

pro-enzyme
no proteolytic activity
but can be activated by cleavage

Question 3

3 effector caspases

Answer 3

caspase 3,6,7

Question 4

4 Initiator caspases

Answer 4

caspase 2,8,9,10

Question 5

Initiation of intrinsic pathway

Answer 5

stress leads to changes in the mitochondrial membrane potential (MMP) due to permeabilization of the outer mitochondrial membrane (OMM)

mitochondria release of Cyt C

Question 6

Components of apoptosome

Answer 6

Cyt C
Apaf-1
Caspase 9

Question 7

Signalling transduction in the intrinsic pathway

Answer 7

Formation of apoptosome

activation of caspase 9

activation of caspases 3, 6, 7

Question 8

Initiation of extrinsic pathway

Answer 8

CD95L ligand binds to CD95 receptor and induces the formation of a trimeric receptor complex

Question 9

Signalling transduction in extrinsic pathway

Answer 9

CD95 binds to DD containing FADD via a DD to DD homotypic interaction

FADD recruits caspase 8 to receptor complex (formation of DISC)

procaspase 8 oligomerization drives self-cleavage to form activated caspase 8 tetramer

activated caspase 8 activates caspase 3, 6, 7

Question 10

Cross talk between extrinsic and intrinsic pathway

Answer 10

activated caspase 8 cleaves Bid to truncated Bid (tBid)

tBid translocated to the mitochondrial membrane and trigger cell death through intrinsic mitochondrial pathway

Question 11

Structure and function of cFLIP

Answer 11

structurally similar to caspase 8

chromosomal localization is in the vicinity of caspase 8 at 2q33

suggest a genetic duplication event

bind to DED of FADD and inhibit FADD caspase 8 interaction

Question 12

BCL-2 family protein and their domain function

Answer 12

BH1 and BH2 - involved in regulation of permeability of outer mitochondrial membrane (OMM)

BH3 - associate with BH1 and BH2, allow homo and heterodimerization

BH4 - intra-cytoplasmic interaction domain for APAF-1

Question 13

Antiapoptotic Bcl-1 family proteins

Answer 13

Bcl-2

Bcl-XL

BH3 only and others are proapoptotic

Question 14

3 domains of IAPs

Answer 14

BIR 1,2,3 - interaction with caspase 3

CARD (caspase recruitment domain) - interact with caspase 8

RING - display E3 ubiquitin ligase activity towards caspase

Question 15

SMAC and DIABLO

Answer 15

acts as dimer and binds to BIR3 domains of IAP to prevent binding to caspases 3

activate apoptosis