Caspase-3 is a
caspase
Caspases (cysteine-aspartic proteases, cysteine aspartases or cysteine-dependent aspartate-directed proteases) are a family of protease enzymes playing essential roles in programmed cell death. They are named caspases due to their specific cyst ...
protein that interacts with
caspase-8
Caspase-8 is a caspase protein, encoded by the ''CASP8'' gene. It most likely acts upon caspase-3.
''CASP8'' orthologs have been identified in numerous mammals for which complete genome data are available. These unique orthologs are also present ...
and
caspase-9
Caspase-9 is an enzyme that in humans is encoded by the CASP9 gene. It is an initiator caspase, critical to the apoptotic pathway found in many tissues. Caspase-9 homologs have been identified in all mammals for which they are known to exist, such ...
. It is encoded by the ''CASP3'' gene. ''CASP3''
orthologs
Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a spe ...
have been identified in numerous
mammals for which complete genome data are available. Unique orthologs are also present in
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s,
lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia al ...
s,
lissamphibians, and
teleost
Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tel ...
s.
The CASP3
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...
is a member of the cysteine-aspartic acid protease (
caspase
Caspases (cysteine-aspartic proteases, cysteine aspartases or cysteine-dependent aspartate-directed proteases) are a family of protease enzymes playing essential roles in programmed cell death. They are named caspases due to their specific cyst ...
) family.
Sequential activation of caspases plays a central role in the execution-phase of
cell apoptosis
Apoptosis (from grc, wikt:ἀπόπτωσις, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemistry, Biochemical events lead to characteristic cell changes (Morp ...
. Caspases exist as inactive
proenzyme
In biochemistry, a zymogen (), also called a proenzyme (), is an inactive precursor of an enzyme. A zymogen requires a biochemical change (such as a hydrolysis reaction revealing the active site, or changing the configuration to reveal the acti ...
s that undergo proteolytic processing at conserved aspartic residues to produce two subunits, large and small, that dimerize to form the active
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...
. This protein cleaves and activates
caspases 6 and
7; and the protein itself is processed and activated by caspases 8, 9, and
10. It is the predominant caspase involved in the cleavage of
amyloid-beta 4A precursor protein, which is associated with neuronal death in
Alzheimer's disease. Alternative splicing of this gene results in two transcript variants that encode the same protein.
Caspase-3 shares many of the typical characteristics common to all currently-known caspases. For example, its active site contains a
cysteine
Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile.
When present as a deprotonated catalytic residue, s ...
residue (Cys-163) and
histidine
Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated –NH3+ form under biological conditions), a carboxylic acid group (which is in the ...
residue (His-121) that stabilize the
peptide bond
In organic chemistry, a peptide bond is an amide type of covalent chemical bond linking two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 ( nitrogen number two) of another, along a peptide or protein c ...
cleavage of a protein sequence to the carboxy-terminal side of an
aspartic acid
Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α- amino acid that is used in the biosynthesis of proteins. Like all other amino acids, it contains an amino group and a carboxylic acid. Its α-amino group is in the pr ...
when it is part of a particular 4-amino acid sequence.
This specificity allows caspases to be incredibly selective, with a 20,000-fold preference for aspartic acid over
glutamic acid
Glutamic acid (symbol Glu or E; the ionic form is known as glutamate) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can syn ...
.
A key feature of caspases in the cell is that they are present as
zymogens, termed procaspases, which are inactive until a biochemical change causes their activation. Each procaspase has an N-terminal large subunit of about 20 kDa followed by a smaller subunit of about 10 kDa, called p20 and p10, respectively.
Substrate specificity
Under normal circumstances, caspases recognize tetra-peptide sequences on their
substrates and
hydrolyze
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolysis ...
peptide bonds after
aspartic acid
Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α- amino acid that is used in the biosynthesis of proteins. Like all other amino acids, it contains an amino group and a carboxylic acid. Its α-amino group is in the pr ...
residues. Caspase 3 and
caspase 7
Caspase-7, apoptosis-related cysteine peptidase, also known as CASP7, is a human protein encoded by the ''CASP7'' gene.
''CASP7'' orthologs have been identified in nearly all mammals for which complete genome data are available. Unique orthologs ...
share similar substrate specificity by recognizing tetra-peptide motif Asp-x-x-Asp.
The C-terminal Asp is absolutely required while variations at other three positions can be tolerated.
Caspase substrate specificity has been widely used in caspase based
inhibitor
Inhibitor or inhibition may refer to:
In biology
* Enzyme inhibitor, a substance that binds to an enzyme and decreases the enzyme's activity
* Reuptake inhibitor, a substance that increases neurotransmission by blocking the reuptake of a neurotra ...
and drug design.
Structure
Caspase-3, in particular, (also known as CPP32/Yama/apopain)
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
The beta sheet, (β-sheet) (also β-pleated sheet) is a common motif of the regular protein secondary structure. Beta sheets consist of beta strands (β-strands) connected laterally by at least two or three backbone hydrogen bonds, forming a gen ...
structure surrounded by
alpha-helices
The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues earli ...
that is unique to caspases.
When the heterodimers align head-to-tail with each other, an active site is positioned at each end of the molecule formed by residues from both participating subunits, though the necessary Cys-163 and His-121 residues are found on the p17 (larger) subunit.
Mechanism
The catalytic site of caspase-3 involves the thiol group of Cys-163 and the
imidazole
Imidazole (ImH) is an organic compound with the formula C3N2H4. It is a white or colourless solid that is soluble in water, producing a mildly alkaline solution. In chemistry, it is an aromatic heterocycle, classified as a diazole, and has non ...
ring of His-121. His-121 stabilizes the
carbonyl
In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containin ...
group of the key aspartate residue, while Cys-163 attacks to ultimately cleave the peptide bond. Cys-163 and Gly-238 also function to stabilize the tetrahedral
transition state
In chemistry, the transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest potential energy along this reaction coordinate. It is often marked ...
of the substrate-enzyme complex through
hydrogen bonding
In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing ...
.
In vitro
''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology and ...
, 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).
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.
Activation
Caspase-3 is activated in the apoptotic cell both by extrinsic (death ligand) and intrinsic (mitochondrial) pathways.
The zymogen feature of caspase-3 is necessary because if unregulated, caspase activity would kill cells indiscriminately.
As an executioner caspase, the caspase-3 zymogen has virtually no activity until it is cleaved by an initiator caspase after apoptotic signaling events have occurred.
One such signaling event is the introduction of
granzyme B, which can activate initiator caspases, into cells targeted for apoptosis by killer
T cells
A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell ...
.
This extrinsic activation then triggers the hallmark caspase cascade characteristic of the apoptotic pathway, in which caspase-3 plays a dominant role.
In intrinsic activation,
cytochrome c
The cytochrome complex, or cyt ''c'', is a small hemeprotein found loosely associated with the inner membrane of the mitochondrion. It belongs to the cytochrome c family of proteins and plays a major role in cell apoptosis. Cytochrome c is hig ...
from the
mitochondria works in combination with
caspase-9
Caspase-9 is an enzyme that in humans is encoded by the CASP9 gene. It is an initiator caspase, critical to the apoptotic pathway found in many tissues. Caspase-9 homologs have been identified in all mammals for which they are known to exist, such ...
, apoptosis-activating factor 1 (
Apaf-1
Apoptotic protease activating factor 1, also known as APAF1, is a human homolog of ''C. elegans'' CED-4 gene.
Function
The protein was identified in the lab of Xiaodong Wang as an activator of caspase-3 in the presense of cytochromeC and dATP ...
), and
ATP
ATP may refer to:
Companies and organizations
* Association of Tennis Professionals, men's professional tennis governing body
* American Technical Publishers, employee-owned publishing company
* ', a Danish pension
* Armenia Tree Project, non ...
to process procaspase-3.
These molecules are sufficient to activate caspase-3 in vitro, but other regulatory proteins are necessary
in vivo
Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...
.
Mangosteen (''Garcinia mangostana'') extract has been shown to inhibit the activation of caspase 3 in B-amyloid treated human neuronal cells.
Inhibition
One means of caspase inhibition is through the IAP (inhibitor of apoptosis) protein family, which includes c-IAP1, c-IAP2,
XIAP
X-linked inhibitor of apoptosis protein (XIAP), also known as inhibitor of apoptosis protein 3 (IAP3) and baculoviral IAP repeat-containing protein 4 (BIRC4), is a protein that stops apoptotic cell death. In humans, this protein (XIAP) is produc ...
, and ML-IAP.
XIAP binds and inhibits initiator caspase-9, which is directly involved in the activation of executioner caspase-3.
During the caspase cascade, however, caspase-3 functions to inhibit XIAP activity by cleaving caspase-9 at a specific site, preventing XIAP from being able to bind to inhibit caspase-9 activity.
Interactions
Caspase 3 has been shown to
interact with:
*
CASP8
*
NMT2
*
CFLAR
CASP8 and FADD-like apoptosis regulator is a protein that in humans is encoded by the ''CFLAR'' gene. Also called c-FLIP (FLICE
Caspase-8 is a caspase protein, encoded by the ''CASP8'' gene. It most likely acts upon caspase-3.
''CASP8'' ortholo ...
*
DCC
*
GroEL
GroEL is a protein which belongs to the chaperonin family of molecular chaperones, and is found in many bacteria. It is required for the proper folding of many proteins. To function properly, GroEL requires the lid-like cochaperonin protein c ...
*
HCLS1
Hematopoietic lineage cell-specific protein is a protein that in humans is encoded by the ''HCLS1'' gene.
Interactions
HCLS1 has been shown to interact with Caspase 3
Caspase-3 is a caspase protein that interacts with caspase-8 and caspase-9. I ...
*
Survivin
Survivin, also called baculoviral inhibitor of apoptosis repeat-containing 5 or BIRC5, is a protein that, in humans, is encoded by the ''BIRC5'' gene.
Survivin is a member of the inhibitor of apoptosis (IAP) family. The survivin protein functions ...
*
TRAF3
*
XIAP
X-linked inhibitor of apoptosis protein (XIAP), also known as inhibitor of apoptosis protein 3 (IAP3) and baculoviral IAP repeat-containing protein 4 (BIRC4), is a protein that stops apoptotic cell death. In humans, this protein (XIAP) is produc ...
*
NFE2L2
Nuclear factor erythroid 2-related factor 2 (NRF2), also known as nuclear factor erythroid-derived 2-like 2, is a transcription factor that in humans is encoded by the ''NFE2L2'' gene. NRF2 is a basic leucine zipper (bZIP) protein that may regula ...
Biological function
Caspase-3 has been found to be necessary for normal
brain
The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special ...
development as well as its typical role in apoptosis, where it is responsible for
chromatin
Chromatin is a complex of DNA and protein found in eukaryote, eukaryotic cells. The primary function is to package long DNA molecules into more compact, denser structures. This prevents the strands from becoming tangled and also plays important ...
condensation and
DNA fragmentation.
Elevated levels of a fragment of Caspase-3, p17, in the bloodstream is a sign of a recent
myocardial infarction
A myocardial infarction (MI), commonly known as a heart attack, occurs when blood flow decreases or stops to the coronary artery of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which ...
.
It is now being shown that caspase-3 may play a role in embryonic and hematopoietic
stem cell
In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of ...
differentiation.
See also
*
The Proteolysis Map
The Proteolysis MAP (PMAP) is an integrated web resource focused on proteases.
Rationale
PMAP is to aid the protease researchers in reasoning about proteolytic networks and metabolic pathways.
History and funding
PMAP was originally create ...
*
Caspase
Caspases (cysteine-aspartic proteases, cysteine aspartases or cysteine-dependent aspartate-directed proteases) are a family of protease enzymes playing essential roles in programmed cell death. They are named caspases due to their specific cyst ...
*
PAC-1
References
Further reading
*
*
*
*
*
External links
* The
MEROPS
MEROPS is an online database for peptidases (also known as proteases, proteinases and proteolytic enzymes) and their inhibitors. The classification scheme for peptidases was published by Rawlings & Barrett in 1993, and that for protein inhibi ...
online database for peptidases and their inhibitors
C14.003
Apoptosis & Caspase 3–
The Proteolysis Map
The Proteolysis MAP (PMAP) is an integrated web resource focused on proteases.
Rationale
PMAP is to aid the protease researchers in reasoning about proteolytic networks and metabolic pathways.
History and funding
PMAP was originally create ...
-animation
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