MSR1
Encyclopedia
Macrophage 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 (cluster of differentiation
204).
scavenger receptor
s, which include three different types (1, 2, 3) generated by alternative splicing of this gene. These receptors or isoforms are trimeric integral membrane glycoprotein
s and have been implicated in many macrophage-associated physiological and pathological processes including atherosclerosis, Alzheimer's disease
, and host defense. They were thought to be expressed macrophage-specific, but recently shown to be present on different dendritic cells classes, too.
The isoforms type 1 and type 2 are functional receptors and are able to mediate the endocytosis of modified low density lipoprotein
s (LDLs). The isoform type 3 does not internalize modified LDL (acetyl-LDL) despite having the domain shown to mediate this function in the types 1 and 2 isoforms. It has an altered intracellular processing and is trapped within the endoplasmic reticulum
, making it unable to perform endocytosis
. The isoform type 3 can inhibit the function of isoforms type 1 and type 2 when co-expressed, indicating a dominant negative effect and suggesting a mechanism for regulation of scavenger receptor activity in macrophages.
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
which in humans is encoded by the MSR1 gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
.
MSR1 has also recently been designated CD204 (cluster of differentiation
Cluster of differentiation
The cluster of differentiation is a protocol used for the identification and investigation of cell surface molecules present on white blood cells, providing targets for immunophenotyping of cells...
204).
Function
This gene encodes the class A macrophageMacrophage
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...
scavenger receptor
Scavenger receptor
Scavenger receptors are a group of receptors that recognize modified low-density lipoprotein by oxidation or acetylation. This naming is based on a function of cleaning : Scavenger receptors widely recognize and uptake macromolecules having a negative charge as well as modified LDL.-Function:It is...
s, which include three different types (1, 2, 3) generated by alternative splicing of this gene. These receptors or isoforms are trimeric integral membrane glycoprotein
Glycoprotein
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...
s and have been implicated in many macrophage-associated physiological and pathological processes including atherosclerosis, Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
, and host defense. They were thought to be expressed macrophage-specific, but recently shown to be present on different dendritic cells classes, too.
The isoforms type 1 and type 2 are functional receptors and are able to mediate the endocytosis of modified low density lipoprotein
Low density lipoprotein
Low-density lipoprotein is one of the five major groups of lipoproteins, which in order of size, largest to smallest, are chylomicrons, VLDL, IDL, LDL, and HDL, that enable transport of cholesterol within the water-based bloodstream...
s (LDLs). The isoform type 3 does not internalize modified LDL (acetyl-LDL) despite having the domain shown to mediate this function in the types 1 and 2 isoforms. It has an altered intracellular processing and is trapped within the endoplasmic reticulum
Endoplasmic reticulum
The endoplasmic reticulum is an organelle of cells in eukaryotic organisms that forms an interconnected network of tubules, vesicles, and cisternae...
, making it unable to perform endocytosis
Endocytosis
Endocytosis is a process by which cells absorb molecules by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane...
. The isoform type 3 can inhibit the function of isoforms type 1 and type 2 when co-expressed, indicating a dominant negative effect and suggesting a mechanism for regulation of scavenger receptor activity in macrophages.