Question

 2. Explain how two procaspases become one active caspase.

 3. What role does cvtochome play in apoptosis?

 4. Why does a caspase cascade ampify the orainal apoptotic stimulus?

 5. What is the function of BCL2 protein in the cel? f8 fg ho 1

Answer 1

For question 2 and 3 figure is provided as well.

2) Explain how two procaspases become one active caspase:

Caspases (Cys dependent aspartate specific protease) are so named because they contain a key cysteine residue in the catalytic site and selectively cleave protein at C- terminus to aspartate residue. Pro- caspases are inactive form of caspase, in many multicellular organisms, many enzymes in an inactive form and in order they make them themselves active, they follow the cascades of reaction.

Initially procaspase is present in form of homodimer, containing C and N terminus, Homodimer of procaspase splits into a small and large and small subunit that form heterodimer two such dimers assembled to form active tetramer. Once activated, caspases cleave and thereby activate other procaspases, resulting in amplifying proteolytic cascade. The procaspases that act as the start of proteolytic cascade are called initiator procaspases; when activated they cleave and activated downstream executioner procaspases.

3) What role cytochrome does play in apoptosis?

There is two type of apoptotic pathways; Extrinsic pathway and Intrinsic pathway.

In intrinsic apoptotic pathway mitochondria play a central by releasing Cytochrome c. once in cytoplasm, Cytochrome c binds to adaptor protein Apaf-1 (Apoptotic protease activating factor) a mammalian homologues of C.elegans CED-4 protein. The basic role Cytochrome c is to trigger the activation of caspase 9 , C cytochrome interact with apaf-1, datp/ATP and procaspase 9 to form complex as the apoptosome. The incorporation of procaspase9 in the apoptosome trigger the auto activating cleavage. Caspase 9 in turn, cleave of procaspase -3 to generate caspase 3, which cleave target that cause apoptosis of the cell.

4) why does caspase cascade amplify the original apoptotic stimulus:

As I suggested in previous answers, activated caspase act as the catalyst to initialize procaspase activation reaction. This is twostep process which help caspase to act as the stimulator for apoptosis. Only activation of caspases can have led the further apoptotic reaction by using following mechanism

Dimerisation:

The activation of caspase initiated be the dimerization, in this reaction adaptor protein and protein- protein interaction motifs take part and collectively facilitate the formation of death fold, which is know as pro domain. The pro-domain of the intrinsic initiator caspases called as caspase recruitment domain (CARD) which contain single death domain. while pro-domain of the extrinsic initiator caspases contains two death folds known as death effector domains (DED).

Cleavage: After complete dimiratisation, the Caspases cleave at inter domain linker regions, and farm large and small subunit. This cleavage allows the active-site loops to take up a conformation of enzymatic activity.

5) Function of BCL2 protein in the cell:

BCL2 is the member of anti-apoptotic protein family such as Bcl-2, Bcl-xl. Bcl2 family of protein regulate the intrinsic pathway of apoptosis, the Bcl2 family (Bcl-2 stands for B cell lymphoma/leukemia 2 gene). mammalian Bcl2 family of protein regulate the intrinsic pathways of apoptosis by controlling the release of Cytochrome c can other intermembrane mitochondrial protein into the cytosol.

The pro- apoptotic Bcl2 consist of two subfamilies:

1. The BH123 protein (Bax and Bak )
2. BH3 only protein (Bid, Bim, Bif, Bad, BmF)

when apoptotic stimulus intriguer the intrinsic pathway, the pro-apoptotic BH123 become activated and induce the release of Cytochrome c, in the absence of apoptotic stimulus, Bcl2 protein bind and inhibit the BH123 protein in the outer membrane of Mitochondria.