Apoptosis controlling overall and Bcl-2

Question 1

What is apoptosis dependent on?

Answer 1

CASPASES - A family of ProteASES that have a Cysteine at their active site and cleave their target proteins at specific ASpartic acids.

Question 2

What do caspases do once active?

Answer 2

Activate other caspases - an amplifying proteolytic cascade

Question 3

What is an amplifying proteolytic cascade?

Answer 3

Caspases activating other caspases

Question 4

What are the 2 ways caspases are activated?

Answer 4

From OUTSIDE the cell by activation of death receptors on the cell surface or suicide.

Question 5

What is the first step of the EXTRINSIC mechanism? The first stage.

Answer 5

Killer lymphocytes carrying Fas ligand binds and activates Fas proteins on the surface of target cells.

Question 6

What is a Fas ligand?

Answer 6

Fas ligand s a type-II transmembrane protein that belongs to the tumor necrosis factor (TNF) family. Its binding with its receptor induces apoptosis.

Question 7

What is the second step of the extrinsic mechanism?

Answer 7

Adaptor proteins bind to Fas proteins and cause aggregation of PRO-CASPASE-8 molecules.

Question 8

What is the first stage of the INTRINSIC mechanism?

Answer 8

Mitochondria release cytochromc C, which binds and caused aggregation of Apaf-1

Question 9

What is the second stage of the intrinsic mechanism?

Answer 9

Apaf-1 binds and aggregates procaspase-9 molecules

Question 10

What is the third and final stage of both the extrinsic and intrinsic mechanism?

Answer 10

Procaspase cleaved, triggering caspase cascade.

Question 11

What is BCL-2?

Answer 11

Bcl-2 family are promotors/suppresors of apoptosis; regulators.

Question 12

What are caspases?

Answer 12

Cystine proteases, executioners of apop.

Question 13

Which Bcl-2 family molecules are anti-apop?

Answer 13

Bcl-2 and Bcl-x

Question 14

Which Bcl-2 family molecules are pro-apop?

Answer 14

Bax, Bak, Bid, Bim

Question 15

Where do Bcl-2 family reside?

Answer 15

Mitochondrial membrane

Question 16

What can pro-apop Bcl fam molecules stimulate?

Answer 16

They can stimulate release of cyt-c OR inactivate death-inihibiting members of the fam

Question 17

Which of the two, pro/anti apop members can be heterodimers?

Answer 17

Both

Question 18

How does Anti-apop block pro-apop’s activity?

Answer 18

Dimers with it

Question 19

What determines whether a cell will live or die?

Answer 19

Relative levels of pro/anti

Question 20

Describe the structure of Bcl-Xl

Answer 20

7 alpha helices in 3 layers - 2 central surrounded by amphipathic.

Question 21

Is Bcl-Xl an inhibitor or promoter of apop?

Answer 21

Inhbitor

Question 22

What does Bcl-Xl resemble?

Answer 22

Bacterial toxins - they have central alpha helices to penetrate membranes and form channels whereas Bcl-2 family forms pH dependent ion conducting channels.

Question 23

What kind of channels does the Bcl-2 family form?

Answer 23

pH-dependent ion conducting channels

Question 24

How does the Bcl-2 family regulate programmed cell death?

Answer 24

DIMERISATION

Question 25

What of the Bcl-2 family is functionally important?

Answer 25

4 homology regions - Bcl1, Bcl2, Bcl3, Bcl4. Bcl1-3 cluster on one side of the molecule and form a hydrophobic patch

Question 26

Which homology region(s) is required for Bak/Bax dimerisation?

Answer 26

BH3

Question 27

What does Bak bind to and via what kind of peptide?

Answer 27

Bcl-Xl via a 16 residue BH3 containing peptide as an alpha helix that fits into a hydrophobic cleft formed by residues in the BH1-3 regions of Bcl-Xl

Question 28

What form interactions play a part in dimerisation? And which form plays a part with the Bak BH3 helix?

Answer 28

Electrostatic AND hydrophobic. and hydrophobic residues of Bak BH3 helix that face the protein contribute to the complex formation. The Leu78 of Bak interacts extensively with Bcl-Xl

Question 29

What happens if the Leu of Bak mutates to an Al?

Answer 29

Binding affinity for Bcl-Xl reduces 800 fold. CANCER.

Question 30

What contributes to the specificity of the Bcl-Xl-Bak interaction?

Answer 30

Salt-bridges

Question 31

What mediates Bcl-2 proteins interaction with other proteins?

Answer 31

BH4