Apoptosis controlling overall and Bcl-2 Flashcards
What is apoptosis dependent on?
CASPASES - A family of ProteASES that have a Cysteine at their active site and cleave their target proteins at specific ASpartic acids.
What do caspases do once active?
Activate other caspases - an amplifying proteolytic cascade
What is an amplifying proteolytic cascade?
Caspases activating other caspases
What are the 2 ways caspases are activated?
From OUTSIDE the cell by activation of death receptors on the cell surface or suicide.
What is the first step of the EXTRINSIC mechanism? The first stage.
Killer lymphocytes carrying Fas ligand binds and activates Fas proteins on the surface of target cells.
What is a Fas ligand?
Fas ligand s a type-II transmembrane protein that belongs to the tumor necrosis factor (TNF) family. Its binding with its receptor induces apoptosis.
What is the second step of the extrinsic mechanism?
Adaptor proteins bind to Fas proteins and cause aggregation of PRO-CASPASE-8 molecules.
What is the first stage of the INTRINSIC mechanism?
Mitochondria release cytochromc C, which binds and caused aggregation of Apaf-1
What is the second stage of the intrinsic mechanism?
Apaf-1 binds and aggregates procaspase-9 molecules
What is the third and final stage of both the extrinsic and intrinsic mechanism?
Procaspase cleaved, triggering caspase cascade.
What is BCL-2?
Bcl-2 family are promotors/suppresors of apoptosis; regulators.
What are caspases?
Cystine proteases, executioners of apop.
Which Bcl-2 family molecules are anti-apop?
Bcl-2 and Bcl-x
Which Bcl-2 family molecules are pro-apop?
Bax, Bak, Bid, Bim
Where do Bcl-2 family reside?
Mitochondrial membrane
What can pro-apop Bcl fam molecules stimulate?
They can stimulate release of cyt-c OR inactivate death-inihibiting members of the fam
Which of the two, pro/anti apop members can be heterodimers?
Both
How does Anti-apop block pro-apop’s activity?
Dimers with it
What determines whether a cell will live or die?
Relative levels of pro/anti
Describe the structure of Bcl-Xl
7 alpha helices in 3 layers - 2 central surrounded by amphipathic.
Is Bcl-Xl an inhibitor or promoter of apop?
Inhbitor
What does Bcl-Xl resemble?
Bacterial toxins - they have central alpha helices to penetrate membranes and form channels whereas Bcl-2 family forms pH dependent ion conducting channels.
What kind of channels does the Bcl-2 family form?
pH-dependent ion conducting channels
How does the Bcl-2 family regulate programmed cell death?
DIMERISATION
What of the Bcl-2 family is functionally important?
4 homology regions - Bcl1, Bcl2, Bcl3, Bcl4. Bcl1-3 cluster on one side of the molecule and form a hydrophobic patch
Which homology region(s) is required for Bak/Bax dimerisation?
BH3
What does Bak bind to and via what kind of peptide?
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
What form interactions play a part in dimerisation? And which form plays a part with the Bak BH3 helix?
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
What happens if the Leu of Bak mutates to an Al?
Binding affinity for Bcl-Xl reduces 800 fold. CANCER.
What contributes to the specificity of the Bcl-Xl-Bak interaction?
Salt-bridges
What mediates Bcl-2 proteins interaction with other proteins?
BH4
