Stromelysin-1 also known as matrix metalloproteinase-3 (MMP-3) is an
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
that in humans is encoded by the ''MMP3''
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
. The MMP3 gene is part of a cluster of MMP genes which localize to chromosome 11q22.3. MMP-3 has an estimated molecular weight of 54 kDa.
Function
Proteins of the matrix metalloproteinase (
MMP) family are involved in the breakdown of
extracellular matrix
In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide stru ...
proteins and during tissue remodeling in normal physiological processes, such as embryonic development and reproduction, as well as in disease processes, such as arthritis, and
tumour metastasis. Most MMPs are secreted as inactive proproteins which are activated when cleaved by extracellular proteinases.
The MMP-3 enzyme degrades
collagen
Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...
types II, III, IV, IX, and X,
proteoglycan
Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan (GAG) chain(s). The point of attachment is a serine (Ser) residue to whic ...
s,
fibronectin
Fibronectin is a high- molecular weight (~500-~600 kDa) glycoprotein of the extracellular matrix that binds to membrane-spanning receptor proteins called integrins. Fibronectin also binds to other extracellular matrix proteins such as collage ...
,
laminin
Laminins are a family of glycoproteins of the extracellular matrix of all animals. They are major components of the basal lamina (one of the layers of the basement membrane), the protein network foundation for most cells and organs. The laminins ...
, and
elastin
Elastin is a protein that in humans is encoded by the ''ELN'' gene. Elastin is a key component of the extracellular matrix in gnathostomes (jawed vertebrates). It is highly elastic and present in connective tissue allowing many tissues in the bod ...
. In addition, MMP-3 can also activate other MMPs such as
MMP-1
Interstitial collagenase, also known as fibroblast collagenase, and matrix metalloproteinase-1 (MMP-1) is an enzyme that in humans is encoded by the ''MMP1'' gene. The gene is part of a cluster of MMP genes which localize to chromosome 11q22.3. ...
,
MMP-7
Matrilysin also known as matrix metalloproteinase-7 (MMP-7), pump-1 protease (PUMP-1), or uterine metalloproteinase is an enzyme in humans that is encoded by the ''MMP7'' gene. The enzyme () has also been known as ''matrin'', ''putative (or punctu ...
, and
MMP-9
Matrix metallopeptidase 9 (MMP-9), also known as 92 kDa type IV collagenase, 92 kDa gelatinase or gelatinase B (GELB), is a matrixin, a class of enzymes that belong to the zinc-metalloproteinases family involved in the degradation of the extracel ...
, rendering MMP-3 crucial in connective tissue remodeling.
The enzyme is also thought to be involved in wound repair, progression of atherosclerosis, and tumor initiation.
In addition to classical roles for MMP3 in extracellular space, MMP3 can enter in cellular nuclei and control transcription.
Gene regulation
MMP3 itself can enter in nuclei of cells and regulate target gene such as CTGF/CCN2 gene.
Expression of MMP3 is primarily regulated at the level of transcription, where the
promoter of the gene responds to various stimuli, including
growth factor
A growth factor is a naturally occurring substance capable of stimulating cell proliferation, wound healing, and occasionally cellular differentiation. Usually it is a secreted protein or a steroid hormone. Growth factors are important for regu ...
s,
cytokine
Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in autocrin ...
s, tumor promoters, and
oncogene
An oncogene is a gene that has the potential to cause cancer. In tumor cells, these genes are often mutated, or expressed at high levels. products.
A
polymorphism in the promoter of the MMP3 gene was first reported in 1995.
The polymorphism is caused by a variation in the number of
adenosine
Adenosine ( symbol A) is an organic compound that occurs widely in nature in the form of diverse derivatives. The molecule consists of an adenine attached to a ribose via a β-N9-glycosidic bond. Adenosine is one of the four nucleoside building ...
s located at position -1171 relative to the transcription start site, resulting in one
allele
An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution.
::"The chro ...
having five adenosines (5A) and the other allele having six adenosines (6A). In vitro promoter functional analyses showed that the 5A allele had greater promoter activities as compared with the 6A allele.
It has been shown in different studies that individuals carrying the 5A allele have increased susceptibility to diseases attributed to increased MMP expression, such as
acute 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 may tr ...
and
abdominal aortic aneurysm
Abdominal aortic aneurysm (AAA) is a localized enlargement of the abdominal aorta such that the diameter is greater than 3 cm or more than 50% larger than normal. They usually cause no symptoms, except during rupture. Occasionally, abdominal, ...
.
On the other hand, the 6A allele has been found to be associated with diseases characterized by insufficient MMP-3 expression due to a lower promoter activity of the 6A allele, such as progressive
coronary atherosclerosis
Atherosclerosis is a pattern of the disease arteriosclerosis in which the wall of the artery develops abnormalities, called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque. At onset there are usually no sy ...
.
The -1171 5A/6A variant has also been associated with congenital anomalies such as
cleft lip and palate
A cleft lip contains an opening in the upper lip that may extend into the nose. The opening may be on one side, both sides, or in the middle. A cleft palate occurs when the palate (the roof of the mouth) contains an opening into the nose. The ...
, where individuals with cleft lip/palate presented significantly more 6A/6A genotypes than controls.
Recently, the MMP3 gene was shown to be down-regulated in individuals with
cleft lip and palate
A cleft lip contains an opening in the upper lip that may extend into the nose. The opening may be on one side, both sides, or in the middle. A cleft palate occurs when the palate (the roof of the mouth) contains an opening into the nose. The ...
when compared to controls,
reinforcing the nature of cleft lip/palate as a condition resulting from insufficient or defective embryonic tissue remodeling.
Structure
![MMP_structures](https://upload.wikimedia.org/wikipedia/commons/0/0f/MMP_structures.gif)
Most members of the MMP family are organized into three basic, distinctive, and well-conserved domains based on structural considerations: an amino-terminal
propeptide
A protein precursor, also called a pro-protein or pro-peptide, is an inactive protein (or peptide) that can be turned into an active form by post-translational modification, such as breaking off a piece of the molecule or adding on another molecule ...
; a catalytic domain; and a
hemopexin
Hemopexin (or haemopexin; Hpx; Hx), also known as beta-1B-glycoprotein, is a glycoprotein that in humans is encoded by the ''HPX'' gene and belongs to the hemopexin family of proteins. Hemopexin is the plasma protein with the highest binding affi ...
-like domain at the carboxy-terminal. The propeptide consists of approximately 80–90 amino acids containing a cysteine residue, which interacts with the catalytic zinc atom via its side chain thiol group. A highly conserved sequence (. . .PRCGXPD. . .) is present in the propeptide. Removal of the propeptide by
proteolysis
Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Uncatalysed, the hydrolysis of peptide bonds is extremely slow, taking hundreds of years. Proteolysis is typically catalysed by cellular enzymes called protease ...
results in
zymogen
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 active ...
activation, as all members of the MMP family are produced in a latent form.
The catalytic domain contains two zinc ions and at least one calcium ion coordinated to various residues. One of the two zinc ions is present in the
active site
In biology and biochemistry, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction. The active site consists of amino acid residues that form temporary bonds with the substrate (binding site) a ...
and is involved in the catalytic processes of the MMPs. The second zinc ion (also known as structural zinc) and the calcium ion are present in the catalytic domain approximately 12 Å away from the catalytic zinc. The catalytic zinc ion is essential for the proteolytic activity of MMPs; the three histidine residues that coordinate with the catalytic zinc are conserved among all the MMPs. Little is known about the roles of the second zinc ion and the calcium ion within the catalytic domain, but the MMPs are shown to possess high affinities for structural zinc and calcium ions.
![TIMP-1 in complex with MMP-3](https://upload.wikimedia.org/wikipedia/commons/f/f5/TIMP-1_in_complex_with_MMP-3.png)
The catalytic domain of MMP-3 can be inhibited by
tissue inhibitors of metalloproteinases (TIMPs). The n-terminal fragment of the TIMP binds in the active site cleft much like the peptide substrate would bind. The Cys1 residue of the TIMP
chelates
Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands are ...
to the catalytic zinc and forms
hydrogen bond
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 a ...
s with one of the carboxylate oxygens of the catalytic glutamate residue (Glu202, see mechanism below). These interactions force the zinc-bound water molecule that is essential to the enzyme's function to leave the enzyme. The loss of the water molecule and the blocking of the active site by TIMP disable the enzyme.
The hemopexin-like domain of MMPs is highly conserved and shows sequence similarity to the plasma protein, hemopexin. The hemopexin-like domain has been shown to play a functional role in substrate binding and/or in interactions with the tissue inhibitors of metalloproteinases (TIMPs), a family of specific MMP protein inhibitors.
Mechanism
The mechanism for MMP-3 is a variation on a larger theme seen in all matrix metalloproteinases. In the active site, a water molecule is
coordinated to a glutamate residue (Glu202) and one of the zinc ions present in the catalytic domain. First, the coordinated water molecule performs a
nucleophilic attack
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...
on the peptide substrate's
scissile carbon while the glutamate simultaneously abstracts a proton from the water molecule. The abstracted proton is then removed from the glutamate by the nitrogen of the scissile amide. This forms a tetrahedral gem-diolate intermediate that is coordinated to the zinc atom.
In order for the amide product to be released from the active site, the scissile amide must abstract a second proton from the coordinated water molecule. Alternatively, it has been shown for
thermolysin
Thermolysin (, ''Bacillus thermoproteolyticus neutral proteinase'', ''thermoase'', ''thermoase Y10'', ''TLN'') is a thermostable neutral metalloproteinase enzyme produced by the Gram-positive bacteria ''Bacillus thermoproteolyticus''. It requires ...
(another metalloproteinase) that the amide product can be released in its neutral (R-NH2) form.
The carboxylate product is released after a water molecule attacks the zinc ion and displaces the carboxylate product. The release of the carboxylate product is thought to be the rate-limiting step in the reaction.
In addition to the water molecule directly involved in the mechanism, a second water molecule is suggested to be a part of the MMP-3 active site. This auxiliary water molecule is thought to stabilize the gem-diolate intermediate as well as the transition states by lowering the activation energy for their formation.
This is demonstrated in the mechanism and reaction coordinate diagram below.
Disease relevance
MMP-3 has been implicated in exacerbating the effects of
traumatic brain injury
A traumatic brain injury (TBI), also known as an intracranial injury, is an injury to the brain caused by an external force. TBI can be classified based on severity (ranging from mild traumatic brain injury TBI/concussionto severe traumatic b ...
(TBI) through its disruption of the
blood-brain barrier (BBB). Different studies have shown that after the brain undergoes trauma and
inflammation
Inflammation (from la, wikt:en:inflammatio#Latin, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or Irritation, irritants, and is a protective response involving im ...
has begun, MMP production in the brain is increased. In a study conducted using MMP-3
wild type
The wild type (WT) is the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard "normal" allele at a locus, in contrast to that produced by a non-standard, "m ...
(WT) and
knockout (KO) mice, MMP-3 was shown to increase BBB permeability after traumatic injury.
The WT mice were shown to have lower
claudin
Claudins are a family of proteins which, along with occludin, are the most important components of the tight junctions ( zonulae occludentes). Tight junctions establish the paracellular barrier that controls the flow of molecules in the intercel ...
-5 and
occludin
Occludin is an enzyme ( EC 1.6) that oxidizes NADH. It was first identified in epithelial cells as a 65 kDa integral plasma-membrane protein localized at the tight junctions. Together with Claudins, and zonula occludens-1 (ZO-1), occludin has bee ...
levels than the KO mice after TBI. Claudin and occludin are proteins that are essential for the formation of the
tight junction
Tight junctions, also known as occluding junctions or ''zonulae occludentes'' (singular, ''zonula occludens''), are multiprotein junctional complexes whose canonical function is to prevent leakage of solutes and water and seals between the epith ...
s between the cells of the blood-brain barrier. Tissue from uninjured WT and KO mice brains was also treated with active MMP-3. Both the WT and KO tissues showed a drop in claudin-5, occludin, and
laminin
Laminins are a family of glycoproteins of the extracellular matrix of all animals. They are major components of the basal lamina (one of the layers of the basement membrane), the protein network foundation for most cells and organs. The laminins ...
-α1 (a
basal lamina
The basal lamina is a layer of extracellular matrix secreted by the epithelial cells, on which the epithelium sits. It is often incorrectly referred to as the basement membrane, though it does constitute a portion of the basement membrane. The ba ...
protein), suggesting that MMP-3 directly destroys tight junction and basal lamina proteins.
MMP-3 also does damage to the blood-
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...
barrier (BSCB), the functional equivalent of the blood-brain barrier, after
spinal cord injury
A spinal cord injury (SCI) is damage to the spinal cord that causes temporary or permanent changes in its function. Symptoms may include loss of muscle function, sensation, or autonomic function in the parts of the body served by the spinal cor ...
(SCI). In a similar study conducted using MMP-3 WT and KO mice, MMP-3 was shown to increase BSCB permeability, with the WT mice showing greater BSCB permeability than the KO mice after spinal cord injury. The same study also found decreased BSCB permeability when spinal cord tissues were treated with a MMP-3 inhibitor. These results suggest that the presence of MMP-3 serves to increase BSCB permeability after SCI. The study showed that MMP-3 accomplishes this damage by degrading claudin-5, occludin, and
ZO-1
Zonula occludens-1 ZO-1, also known as Tight junction protein-1 is a 220-kD peripheral membrane protein that is encoded by the ''TJP1'' gene in humans. It belongs to the family of ''zonula occludens proteins'' (ZO-1, ZO-2, and ZO-3), which are ti ...
(another tight junction protein), similar to how MMP-3 damages the BBB.
The increase in blood-brain barrier and blood-spinal cord barrier permeability allows for more
neutrophils
Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying in ...
to infiltrate the brain and spinal cord at the site of inflammation.
Neutrophils carry MMP-9., which has also been shown to degrade occludin. This leads to further disruption of the BBB and BSCB
References
Further reading
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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 inhibitor ...
online database for peptidases and their inhibitors
M10.005*
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Matrix metalloproteinases
EC 3.4.24