DEFINITION
Caspase 3 is an highly conserved cysteine-dependent aspartate-specific proteases belonging to the family C14 in the Barrett and Rawlings classification and play a pivotal role in apoptosis
Caspase 3 is a member of the capases familly. There are two major groups of caspases related with apoptosis:
* initiator caspases: caspase -2,-8,-9,-10
* effector caspases: caspase -3,-6,-7
In the table, there is also a third group of caspases:
*inflammatory caspases -1, -5, -8
known for their role in proinflammatory cytokine maturation.
The Inflammatory Caspases: Key Players in the Host Response to Pathogenic Invasion and Sepsis.2006
The two groups (initiator and effector), related in the apoptosis activation pathway, differ in the length and structure of their prodomain. Initiator caspases carry a long prodomain with a DED and a CARD domain (caspase recruitment domain) wich are the link between cell signalling and apoptosis. The CARD domain binds the adapter molecules, the DED cares for the hydrophobic binding of the adapter protein. Initiator caspases (CASP2, CASP8, CASP9, and CASP10) cleave inactive pro-forms of effector caspases, thereby activating them. Effector caspases (CASP3, CASP6, CASP7) in turn cleave other protein substrates within the cell (ROCK , APP , DFF 40), to trigger the apoptotic process
All the caspases cleave preferentially after Asp residues in a peptide substrate, a specificity very rare among proteolytic enzymes. This specificity allows the caspases to perform highly selective proteolytic events in the cytosol of animal cells.
Mammalian caspases: structure, activation, substrates, and functions during apoptosis.1998
Video_Activation of caspase 3 triggered by internal signals and by external signals
In human Caspase 3 gene is localized on the 4 chromosome (location: Chromosome 4 - NC_000004.11 ), in a region of 609 bp on the reverse strand. The mRNA encodes for a 277 aa polypeptide
Official Symbol:CASP3
Other Aliases:CPP32, CPP32B, SCA-1
Other Designations:CASP-3; CPP-32; PARP cleavage protease; SREBP cleavage activity 1; apopain; caspase 3, apoptosis-related cysteine protease; caspase-3; cysteine protease CPP32; procaspase3; protein Yama
Location:4q34
Annotation:Chromosome 4, NC_000004.11 (185548850..185570629, complement)
MIM:600636
CHEMICAL STRUCTURE AND IMAGES
*Caspase-3 is formed from a 32 kDa zymogen that is cleaved into 17 kDa and 12 kDa subunits.
When the procaspase is cleaved at a particular residue, the active heterotetramer can then be formed by hydrophobic interactions, causing four anti-parallel beta-sheets from p17 and two from p12 to come together to make a heterodimer, which in turn interacts with another heterodimer to form the full 12-stranded beta-sheet structure surrounded by alpha-helices that is unique to caspases.
Protein Aminoacids Percentage
Caspase 3 has some remarkable characteristics compared to the average of the human proteins.
First the glu (glutammate)/ gln (glutammine) ratio is biased towards the second aminoacid, pointing at Caspase 3 being syntetized more efficiently when the oxidative metabolism of the cell is good.
Second high proline is join with non proliferating and collagen-syntetizing cells.
Third low methionine means low proteins synthesis (inside the cell), so the only chance is apoptosis.
There is a high abundance of asparagine, aspartate, serine and arginine which determinates a negative charge of -2,5 at neutral ph (Protein Calculator. This justifies the ability of caspase 3 to be active a cellular ph level.
Caspase-3 is active over a broad pH range that is slightly higher (more basic) than many of the other executioner caspases. This broad range indicates that caspase-3 will be fully active under normal and apoptotic cell conditions.
Another interesting analysis is the comparision of the aminoacid composition between caspase 3 and the lysosomial protease as cathepsin and lysosomial glycosilase as alfa-amylase which are released in the last phases of apoptosis after caspase 3 activation. There are some significant differences: Caspase 3 is active on a basic ph level to allow the initial phase of apoptotic cascade or the no-apoptotic functions of caspase 3 in cell metabolism (see Other Functions); the other two lysosomial enzymes become activated at the low pH found in lysosomes or during the last phases of apoptosis process (ph < 4).
SYNTHESIS AND TURNOVER
Protein Synthesis
Expression profile of caspase 3.
ENZYMATIC ACTIVITY
The catalytic site of caspase-3 involves the sulfohydryl group of Cys-285 and the imidazole ring of His-237. His-237 stabilizes the carbonyl group of the key aspartate residue, while Cys-285 attacks to ultimately cleave the peptide bond. Cys-285 and Gly-238 also function to stabilize the tetrahedral transition state of the substrate-enzyme complex through hydrogen bonding. In vitro, caspase-3 has been found to prefer the peptide sequence DEVDG (Asp-Glu-Val-Asp-Gly) with cleavage occurring on the carboxy side of the second aspartic acid residue (between D and G).
BIOLOGICAL FUNCTION
Using loss and gain of function genetically modified mouse models it was demostrated that caspase 3 is required to trigger the apoptosis' cascade in responde to stress stimuli such as FAS signal (external activatio)or mitochondrial signaling pathway (Cyt. C). Caspase 3 −/− mice have reduced viability and display defective neuronal apoptosis and neurological defects. Inactivation of CASP3 dramatically reduces apoptosis in diverse settings, including activation-induced cell death (AICD) of peripheral T cells, as well as chemotherapy-induced apoptosis of oncogenically transformed caspase 3 −/− MEFs
Essential contribution of caspase 3/CPP32 to apoptosis and its associated nuclearchanges
The cysteine protease CASP3 has been shown to participate in programmed cell death (PCD), or apoptosis, affecting lymphoid cells in vitro. In the thymus, negative selection is a mechanism through which developing thymocytes expressing a TcR with high affinity for self peptide-MHC complexes are eliminated by PCD.
Specific activation of the cysteine protease CPP32 during the negative selection of T cells in the thymus.1997
REGULATION
Cellular Localization
Caspase 3 is localizated in the cytosol of the cell.
Subcellular localization of caspase-3 activation correlates with changes in apoptotic morphology in MOLT-4 leukemia cells exposed to X-ray irradiation. 2005
Caspase-3 cleavage and nuclear localization of caspase-activated DNase in human temporal lobe epilepsy
Nuclear translocation of caspase-3 is dependent on its proteolytic activation and recognition of a substrate-like protein(s).2005
Biological Function
Caspase 3 is famous for it role in Apoptosis. It is the most importan effector caspase in the signalling pathway which lead to apoptosis.
Other Functions
h3. Caspase-3 in Neurodevelopment and Differentiation
Neuronal caspase-3 signaling: not only cell death. 2010
Cell death in the developing nervous system is a phenomenon that has been recognized for almost a 100 years. It is estimated that half of the original cell population produced
during nervous system development is eliminated by apoptosis to optimize synaptic connections and remove unnecessary neurons. In the developing nervous system, apoptosis is observed early in neural tube formation and persists during terminal differentiation of the neural network involving neuron, glial and neural progenitor cells. With a few notable exceptions,it seems that neurons predominantly use the intrinsic pathway of apoptosis to undergo cell death and that the central role of caspase-3 in neurodevelopment is highlighted by abnormal brain development in knockout mice with an altered caspase-3 activation.
Recent studies suggest that caspase-3 also functions as a regulatory molecule in neurogenesis and synaptic activity. Knowledge of biochemical pathway(s) for nonapoptotic activation and modulation of caspase-3 has potential implications for the understanding of synaptic failure in the pathophysiology of neurological disorders.
In the context of a nonapoptotic role of caspase-3, suggest that it is involved in neural stem cell differentiation and not only in cell death. In particular,using an in vitro system (primary derived neuronal stem cells), they showed that caspase-3 activity in neuronal progenitors facilitates neurogenesis. They generated clonally derived
neurospheres from the striatum of E14.5 murine embryos and observed a significant increase in caspase-3 activity during neurosphere differentiation. Interestingly, despite caspase-3 activity increase, no cleavage of PARP (a caspase-3 nuclear substrate cleaved during apoptosis) was observed and the caspase-3 inhibition with z-DEVD-fmk did not affect apoptosis during neurosphere differentiation, suggesting that caspase-3 activity during neurogenesis is not associated with cell death.
Finally, the authors hypothesize that caspase-3 could promote neuronal differentiation through the activation of one or more signaling pathways by cleavage of protein kinases involved in cell differentiation. Physiological neuronal function requires the refinement of neuronal circuits by a selective elimination of axons, dendrites and synaptic connections without the death of parental neurons. This elimination, both during development and in adult tissue, can be divided into two classes: small-scale events (elimination of synaptic connections and the local pruning of an axonal or dendritic arbor) and largescale events (elimination of a significant length of the primary axon and of major axon collaterals).
