Why are they called caspases?
They are named caspases due to their specific cysteine protease activity – a cysteine in its active site nucleophilically attacks and cleaves a target protein only after an aspartic acid residue. As of 2009, there are 12 confirmed caspases in humans and 10 in mice, carrying out a variety of cellular functions.
How many Caspases are there in humans?
As of 2009, there are 12 confirmed caspases in humans and 10 in mice, carrying out a variety of cellular functions. The role of these enzymes in programmed cell death was first identified in 1993, with their functions in apoptosis well characterised.
Do all caspases have the same cleavage sites?
However, many of the cleavage sites are similar and can be cleaved by other caspases. For example, caspase 3 and 7 have very similar cleavage sites. In these situations, the use of specific activators and/ or inhibitors of caspase activity is essential to ensuring determination of the correct activity.
What is the function of caspase in cell cycle?
Caspase. This is a form of programmed cell death, occurring widely during development, and throughout life to maintain cell homeostasis. Activation of Caspases ensures that the cellular components are degraded in a controlled manner, carrying out cell death with minimal effect on surrounding tissues.
Where do caspases cleave proteins?
Cleavage. Once appropriately dimerised, the Caspases cleave at inter domain linker regions, forming a large and small subunit. This cleavage allows the active-site loops to take up a conformation favourable for enzymatic activity.
What proteins are cleaved by caspases?
Caspases. Caspases are a family of cysteine proteases that cleave proteins following aspartic acid residues. These proteases exist in a hierarchy with upstream caspases 2, 8, 9, and 10 and downstream caspases 3, 6, and 7.
Do caspases cleave DNA?
Caspase-3-mediated cleavage of ICAD at amino acids Asp-117 and Asp-224 appears to dissociate the CAD:ICAD complex, allowing free CAD to cleave chromosomal DNA.
What are the targets of caspases?
The number of substrate targets identified for individual caspases can vary widely ranging from only a (few) dozen targets for caspases-4, -5, -9, and -14 to hundreds of targets for caspases-1, -2, -3, -6, -7, and -8.
What do caspases cleave?
Caspases are a family of proteases found in all metazoans, including a dozen in humans, that drive the terminal stages of apoptosis as well as other cellular remodeling and inflammatory events. Caspases are named because they are cysteine class enzymes shown to cleave after aspartate residues.
What does caspase do in apoptosis?
Initiator caspases initiate the apoptosis signal while the executioner caspases carry out the mass proteolysis that leads to apoptosis. Inflammatory caspases do not function in apoptosis but are rather involved in inflammatory cytokine signaling and other types of cell death such as pyroptosis.
How do caspases cause fragmentation of DNA?
Activated caspase eventually cleaves and activates pro-caspase-3. Cleaved caspase-3 translocates to the nucleus, where it cleaves substrates such as the DNA repair enzyme PARP and ICAD. Cleavage of ICAD results in the release and activation of CAD, which induces DNA fragmentation.
What does cleaved caspase-3 mean?
Cleaved caspase-3 propagates an apoptotic signal through enzymatic activity on downstream targets, including poly ADP ribose polymerase (PARP) and other substrates (2). In cell biology, caspase-3 antibodies that detect both uncleaved and cleaved versions of the enzyme are strong indicators of cell death induction.
How do proteases break down proteins?
Proteases are involved in digesting long protein chains into shorter fragments by splitting the peptide bonds that link amino acid residues.
How do caspases induce apoptosis?
Apoptosis is mediated by proteolytic enzymes called caspases, which trigger cell death by cleaving specific proteins in the cytoplasm and nucleus. Caspases exist in all cells as inactive precursors, or procaspases, which are usually activated by cleavage by other caspases, producing a proteolytic caspase cascade.
Do caspases cleave peptide bonds?
Each caspase is a cysteine aspartase; it employs a nucleophilic cysteine in its active site to cleave aspartic acid peptide bonds within proteins.
Do caspases cleave phospholipids?
Caspase cleavage releases a nuclear protein fragment that stimulates phospholipid scrambling at the plasma membrane.
What proteins does caspase-9 cleave?
Chr. Caspase-9 belongs to a family of caspases, cysteine-aspartic proteases involved in apoptosis and cytokine signalling. Apoptotic signals cause the release of cytochrome c from mitochondria and activation of apaf-1 (apoptosome), which then cleaves the pro-enzyme of caspase-9 into the active dimer form.
Do caspases cleave phospholipids?
Caspase cleavage releases a nuclear protein fragment that stimulates phospholipid scrambling at the plasma membrane.
How do proteases break down proteins?
Proteases are involved in digesting long protein chains into shorter fragments by splitting the peptide bonds that link amino acid residues.
Which of the following is an anti apoptotic protein?
Anti-apoptotic proteins BCL-2, MCL-1 and A1 summate collectively to maintain survival of immune cell populations both in vitro and in vivo.
What are caspases in biology?
Caspases define a class of cysteinyl proteases belonging to the C14 family of the Barrett and Rawlings classification Barrett (1997). These enzymes have an absolute requirement for an aspartic acid residue in the P1 position of the scissile bond. The caspase gene family thus far contains 11 human members that can be divided into three groups. Group 1 (caspases 1, 4, and 5) is made of enzymes involved in the regulation of inflammation. Group 2 (caspases 2, 3, and 7) and group 3 (caspases 6, 8, 9 and, 10) are composed of caspases regulating apoptosis. Caspases 11 and 12 are murine proteins of which caspases 5 and 4 may be the human counterparts. The latest addition to the human caspases, caspase-14, seems not to be involved in the regulation of apoptosis or inflammation but may play a role in cell differentiation Eckhart et al (2000). Caspase-13, initially mistaken as a human protein Koenig et al (2001), most likely corresponds to the bovine ortholog of human caspase-4.
Why are caspases grouped?
Caspases were originally grouped based on studies demonstrating their functional role in specific biological process. However, many caspases have now been shown to be involved in processes that are distinct from their originally defined functions, blurring the lines between these functional classes (Miura, 2012 ).
How to determine if caspases are active?
In one method, samples for histology are sectioned and immunostained for caspase activity. This method allows observation of an elevated level of caspase in a sample and identification of the cells that contain the activated caspases. It has been used in several studies involving islets [ 45, 82, 149 ]. A second method makes use of a hydrolysis reaction with a reporter molecule attached to a peptide by aspartic acid. Caspases have a unique specificity because they contain a critical cysteine residue that allows them to cleave other proteins at sites next to an aspartic acid residue [ 182 ]. In this assay, intact islet tissue is washed and lysed to free the activated caspase, which then cleaves the reporter molecule-peptide complex, releasing the reporter molecule and resulting in a color change or fluorescence. This type of assay can be completed in several hours and has been applied to several islet studies in order to quantify caspase activity [ 26, 105, 183, 195 ].
How do caspases detect apoptosis?
When cells are exposed to pro-apoptotic stimuli, a cascade of events begins in which one or more caspases are activated. By measuring the amount of activated caspase (s), one can detect whether or not apoptosis is occurring [ 182 ]. It is necessary to choose in advance the caspase (s) to be assayed. For example, caspase 8 and 9 both initiate the cascade of events, but caspase 8 is usually activated by external signals via membrane death receptors whereas caspase 9 is usually activated by cytotoxic agents that damage mitochondria, allowing cytochrome c leakage into the cytosol [ 182 ]. Caspase 3 and 7 are common downstream effector caspases associated with some forms of β-cell apoptosis [ 26, 45, 105, 149, 183, 195 ].
What is the role of caspases in apoptosis?
Recent evidence indicates that some of the caspases involved in the induction of apoptosis in some cellular systems are required for differentiation programs in others. Survival of cells having activated their caspases is not totally understood but may be mediated by the cleavage of unconventional caspase substrates, such as RasGAP, that generate anti-apoptotic signals once cleaved Yang and Widmann (2001).
How many caspases are there in the human genome?
The caspase gene family thus far contains 11 human members that can be divided into three groups. Group 1 (caspases 1, 4, and 5) is made of enzymes involved in the regulation of inflammation. Group 2 (caspases 2, 3, and 7) and group 3 (caspases 6, 8, 9 and, 10) are composed of caspases regulating apoptosis.
What are the functions of caspases?
Mammalian caspases are categorized into two functional groups, those involved in immunity and those that facilitate apoptotic cell death. Caspases are expressed as inactive precursors inside cells and must be activated to cleave specific target substrates. Pro-apoptotic caspases cleave a larger subset of intracellular proteins to mediate cell suicide by apoptosis, while caspases involved in immunity can kill cells by alternative non-apoptotic mechanisms. Pro-apoptotic caspases are essential for embryonic development and for normal tissue homeostasis.
Abstract
Caspases are a family of proteases found in all metazoans, including a dozen in humans, that drive the terminal stages of apoptosis as well as other cellular remodeling and inflammatory events. Caspases are named because they are cysteine class enzymes shown to cleave after aspartate residues.
Main
Human caspases are a family of 12 homologous intracellular proteases known for driving cellular state changes such as apoptosis and differentiation, as well as inflammatory responses.
Results
The DegraBase ( http://wellslab.ucsf.edu/degrabase/) is a database comprising about 8000 unique proteolytic cuts identified by the subtiligase-based N-terminomics labeling technology from 33 apoptotic and 11 healthy cellular experiments.
Discussion
These studies highlight the use of proteomics coupled with detailed kinetic and structural analysis to reveal a greater prevalence and promiscuity for cleaving after glutamate residues in apoptosis.
Materials and Methods
The DegraBase ( http://wellslab.ucsf.edu/degrabase/) compiles 8090 unique N-termini from 3206 proteins identified in subtiligase-based positive enrichment mass spectrometry experiments in 11 healthy and apoptotic human cell lines.
Acknowledgements
We thank Guy Salvesen and Scott Snipas at the Sanford Burnham Medical Research Institute for their helpful discussions and repeating some of kinetics with our AFC subtrates.
Author information
Present address: Current address: Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA,
Why is it important to use specific activators and inhibitors of caspase activity?
In these situations, the use of specific activators and/ or inhibitors of caspase activity is essential to ensuring determination of the correct activity. Another important consideration when looking at caspase activation is to ensure that the specific caspase is activated in the sample you have chosen.
Is the signal proportional to the amount of caspase activity present in the sample?
The resulting signal is proportional to the amount of caspase activity present in the sample. However, many of the cleavage sites are similar and can be cleaved by other caspases. For example, caspase 3 and 7 have very similar cleavage sites.
