Scavenger receptor
Encyclopedia
Scavenger receptors are a group of receptors
that recognize modified low-density lipoprotein (LDL) by oxidation
or acetylation
. This naming is based on a function of cleaning (scavenging): Scavenger receptors widely recognize and uptake macromolecule
s having a negative charge as well as modified LDL.
specificity and a variety of receptor molecules.
In atherosclerotic
lesions, macrophage
s that express scavenger receptors on their plasma membrane aggressively uptake the oxidized LDL deposited in the blood vessel wall inside and become foam cells, and they secrete various inflammatory cytokine
s and accelerate the development of atherosclerosis.
-like domain, which is essential for ligand
binding.
Members include:
and scavenger receptor class B1
(SR-B1) are identified as oxidized LDL receptors and classified into class B. Both proteins have two transmembrane domains, and they are concentrated in a specific plasma membrane microdomain, the caveolae
.
Members include:
Receptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
that recognize modified low-density lipoprotein (LDL) by oxidation
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
or acetylation
Acetylation
Acetylation describes a reaction that introduces an acetyl functional group into a chemical compound...
. This naming is based on a function of cleaning (scavenging): Scavenger receptors widely recognize and uptake macromolecule
Macromolecule
A macromolecule is a very large molecule commonly created by some form of polymerization. In biochemistry, the term is applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles...
s having a negative charge as well as modified LDL.
Function
It is thought that scavenger receptors participate in the removal of many foreign substances and waste materials in the living body by extensive ligandLigand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
specificity and a variety of receptor molecules.
In atherosclerotic
Atherosclerosis
Atherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...
lesions, macrophage
Macrophage
Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...
s that express scavenger receptors on their plasma membrane aggressively uptake the oxidized LDL deposited in the blood vessel wall inside and become foam cells, and they secrete various inflammatory cytokine
Cytokine
Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...
s and accelerate the development of atherosclerosis.
Types
Scavenger receptors are categorized into classes A, B, and C according to their structural characteristics.- Class A is mainly expressed in the macrophageMacrophageMacrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...
, and a protein whose molecular weight is about 80 kDa makes a trimerTrimer (chemistry)In chemistry, a trimer is a product derived from three identical precursors. Trimers are typically cyclic. Chemical compounds that often trimerise are aliphatic isocyanates and cyanic acids. Often, trimerization competes with polymerization....
; it is composed of 1) cytosolCytosolThe cytosol or intracellular fluid is the liquid found inside cells, that is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into compartments....
domain, 2) transmembraneTransmembrane proteinA transmembrane protein is a protein that goes from one side of a membrane through to the other side of the membrane. Many TPs function as gateways or "loading docks" to deny or permit the transport of specific substances across the biological membrane, to get into the cell, or out of the cell as...
domain, 3) spacer domain, 4) alpha-helicalAlpha helixA common motif in the secondary structure of proteins, the alpha helix is a right-handed coiled or spiral conformation, in which every backbone N-H group donates a hydrogen bond to the backbone C=O group of the amino acid four residues earlier...
coiled-coilCoiled coilA coiled coil is a structural motif in proteins, in which 2-7 alpha-helices are coiled together like the strands of a rope . Many coiled coil type proteins are involved in important biological functions such as the regulation of gene expression e.g. transcription factors...
domain, 5) collagenCollagenCollagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
-like domain, and 6) cysteineCysteineCysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
-rich domain. - Class B has two transmembrane regions.
- Class C is a transmembrane protein whose N-terminusN-terminal endThe N-terminus refers to the start of a protein or polypeptide terminated by an amino acid with a free amine group . The convention for writing peptide sequences is to put the N-terminus on the left and write the sequence from N- to C-terminus...
is located extracellularly.
Scavenger receptor class A
Scavenger receptors type 1 (SR-A1) and 2 (SR-A2) are trimers with a molecular weight of about 220-250 kDa (the molecular weight of monomeric protein is about 80 kDa). They preferentially bind modified LDL by acetic acid and oxidized LDL. They have a collagenCollagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
-like domain, which is essential for ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
binding.
Members include:
- SCARA1 or MSR1MSR1Macrophage scavenger receptor 1, also known as MSR1, is a protein which in humans is encoded by the MSR1 gene.MSR1 has also recently been designated CD204 .- Function :...
: SR-A1 scavenger receptors have a cysteineCysteineCysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
-rich domain, which can be found in a series of cell surface receptors and soluble proteins, but SR-A2 do not. - SCARA2 or MARCOMARCOMacrophage receptor MARCO is a protein that in humans is encoded by the MARCO gene.-Further reading:...
: Another scavenger receptor class A, MARCO, has collagenCollagenCollagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
-like and cysteineCysteineCysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
-rich domains. - SCARA3
- SCARA4 or COLEC12
- SCARA5
Scavenger receptor class B
CD36CD36
CD36 is an integral membrane protein found on the surface of many cell types in vertebrate animals and is also known as FAT, SCARB3, GP88, glycoprotein IV and glycoprotein IIIb . CD36 is a member of the class B scavenger receptor family of cell surface proteins...
and scavenger receptor class B1
SCARB1
Scavenger receptor class B member 1 also known as SR-BI is a protein that in humans is encoded by the SCARB1 gene. SR-BI functions as a receptor for high-density lipoprotein....
(SR-B1) are identified as oxidized LDL receptors and classified into class B. Both proteins have two transmembrane domains, and they are concentrated in a specific plasma membrane microdomain, the caveolae
Caveolae
In biology, caveolae , which are a special type of lipid raft, are small invaginations of the plasma membrane in many vertebrate cell types, especially in endothelial cells and adipocytes....
.
Members include:
- SCARB1SCARB1Scavenger receptor class B member 1 also known as SR-BI is a protein that in humans is encoded by the SCARB1 gene. SR-BI functions as a receptor for high-density lipoprotein....
. SR-B1 can interact not only with oxidized LDL but also with normal LDL and high-density lipoproteins (HDL). Recent studies have indicated that SR-B1 receptors are involved in HDL metabolism. - SCARB2SCARB2Lysosome membrane protein 2 is a protein that in humans is encoded by the SCARB2 gene.- Clinical significance :SCARB2 is a receptor for two viruses that cause hand, foot, and mouth disease in children, Enterovirus 71 and Coxsackievirus A16....
- SCARB3 or CD36CD36CD36 is an integral membrane protein found on the surface of many cell types in vertebrate animals and is also known as FAT, SCARB3, GP88, glycoprotein IV and glycoprotein IIIb . CD36 is a member of the class B scavenger receptor family of cell surface proteins...
. CD36 has been thought to be implicated in cell adhesionCell adhesionCellular adhesion is the binding of a cell to a surface, extracellular matrix or another cell using cell adhesion molecules such as selectins, integrins, and cadherins. Correct cellular adhesion is essential in maintaining multicellular structure...
, in the phagocytosis of apoptotic cells, and in the metabolismMetabolismMetabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
of long-chain fatty acids. In experimental mice models of atherosclerosis in which the gene for CD36 has been deleted, the mice have a greatly reduced number of atherosclerotic lesions.
Others
Some receptors that can bind to oxidized LDL have been discovered.- CD68CD68CD68 is a glycoprotein which binds to low density lipoprotein.It is expressed on monocytes/macrophages.The mouse equivalent is called "macrosialin".-Use in pathology:...
and its mouse homologueHomology (biology)Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
, macrosialin, has a unique N-terminal mucinMucinMucins are a family of high molecular weight, heavily glycosylated proteins produced by epithelial tissues in most metazoans. Mucins' key characteristic is their ability to form gels; therefore they are a key component in most gel-like secretions, serving functions from lubrication to cell...
-like domain. - MucinMucinMucins are a family of high molecular weight, heavily glycosylated proteins produced by epithelial tissues in most metazoans. Mucins' key characteristic is their ability to form gels; therefore they are a key component in most gel-like secretions, serving functions from lubrication to cell...
is a viscous substance (found in nattoNattois a traditional Japanese food made from soybeans fermented with Bacillus subtilis. It is popular especially as a breakfast food. As a rich source of protein and probiotics, nattō and the soybean paste miso formed a vital source of nutrition in feudal Japan. Nattō can be an acquired taste because...
or okraOkraOkra is a flowering plant in the mallow family. It is valued for its edible green seed pods. The geographical origin of okra is disputed, with supporters of South Asian, Ethiopian and West African origins...
) that is composed of a protein and polysaccharides binding it. A DrosophilaDrosophilaDrosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
class C scavenger receptor (dSR-C1) also has a mucinMucinMucins are a family of high molecular weight, heavily glycosylated proteins produced by epithelial tissues in most metazoans. Mucins' key characteristic is their ability to form gels; therefore they are a key component in most gel-like secretions, serving functions from lubrication to cell...
-like structure. - LectinLectinLectins are sugar-binding proteins that are highly specific for their sugar moieties. They play a role in biological recognition phenomena involving cells and proteins. For example, some viruses use lectins to attach themselves to the cells of the host organism during infection...
-like oxidized LDL receptor-1 (LOX-1) was isolated from an aortic endothelial cell, and recently it has been discovered in macrophageMacrophageMacrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...
s and vascular smooth muscle cells in artery vessels. The expression of LOX-1 is inducted by inflammatory stimuli, so LOX-1 is thought to be involved in the development of atheroscleroticAtherosclerosisAtherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...
lesions.