Biglycan
Encyclopedia
Biglycan is a small leucine-rich repeat
proteoglycan
(SLRP) which is found in a variety of extracellular matrix tissues, including bone
, cartilage
and tendon
. In humans, biglycan is encoded by the BGN gene
.
(CS) or dermatan sulfate (DS), with DS being more abundant in most connective tissue
s. The CS/DS chains are attached at amino acids 5 and 10 in human biglycan. The composition of the GAG chains has been reported as varying according to tissue of origin. Non-glycanated forms of biglycan (no GAG chains) increase with age in human articular cartilage
.
in 1989 because the proteoglycan contained two GAG chains; formerly it was known as proteoglycan-I (PG-I).
has been reported for rat, mouse, bovine and human biglycan core proteins.
, both via the core protein and GAG chains. It has been reported that biglycan interacts more strongly with collagen type II than collagen type I. Biglycan has been reported to compete with decorin
for the same binding site on collagen
.
originating from the same tissue has been reported to be similar.
-like phenotype
with reduced growth rate and lower bone
mass than mice that can express biglycan.
Biglycan core protein binds to the growth factors BMP-4 and influences its bioactivity. It has also been reported that the presence of biglycan is necessary for BMP-4 to exert its effects on osteoblasts. There is also evidence that biglycan binds to TGF-beta 1
Leucine-rich repeat
A leucine-rich repeat is a protein structural motif that forms an α/β horseshoe fold. It is composed of repeating 20–30 amino acid stretches that are unusually rich in the hydrophobic amino acid leucine...
proteoglycan
Proteoglycan
Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan chain. The point of attachment is a Ser residue to which the glycosaminoglycan is joined through a tetrasaccharide bridge...
(SLRP) which is found in a variety of extracellular matrix tissues, including bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
, cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
and tendon
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...
. In humans, biglycan is encoded by the BGN 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...
.
Composition
Biglycan consists of a protein core containing leucine-rich repeat regions and two glycosaminoglycan (GAG) chains consisting of either chondroitin sulfateChondroitin sulfate
Chondroitin sulfate is a sulfated glycosaminoglycan composed of a chain of alternating sugars . It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have over 100 individual sugars, each of which can be sulfated in variable positions and quantities...
(CS) or dermatan sulfate (DS), with DS being more abundant in most connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...
s. The CS/DS chains are attached at amino acids 5 and 10 in human biglycan. The composition of the GAG chains has been reported as varying according to tissue of origin. Non-glycanated forms of biglycan (no GAG chains) increase with age in human articular cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
.
Nomenclature
The name "biglycan" was proposed in an article by Fisher, Termine and Young in an article in the Journal of Biological ChemistryJournal of Biological Chemistry
The Journal of Biological Chemistry is a weekly peer-reviewed scientific journal that was established in 1905. Since 1925 it is published by the American Society for Biochemistry and Molecular Biology. It covers research in any area of biochemistry or molecular biology. The editor-in-chief is...
in 1989 because the proteoglycan contained two GAG chains; formerly it was known as proteoglycan-I (PG-I).
Diversity
The structure of biglycan core protein is highly conserved across species; over 90% homologyHomology (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...
has been reported for rat, mouse, bovine and human biglycan core proteins.
Interactions
Biglycan interacts with 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...
, both via the core protein and GAG chains. It has been reported that biglycan interacts more strongly with collagen type II than collagen type I. Biglycan has been reported to compete with decorin
Decorin
Decorin is a proteoglycan on average 90 - 140 kilodaltons in size.It belongs to the small leucine-rich proteoglycan family and consists of a protein core containing leucine repeats with a glycosaminoglycan chain consisting of either chondroitin sulfate or dermatan sulfate .Decorin is a small...
for the same binding site on collagen
Collagen
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...
.
Similarity to decorin
The composition of GAG chains of biglycan and decorinDecorin
Decorin is a proteoglycan on average 90 - 140 kilodaltons in size.It belongs to the small leucine-rich proteoglycan family and consists of a protein core containing leucine repeats with a glycosaminoglycan chain consisting of either chondroitin sulfate or dermatan sulfate .Decorin is a small...
originating from the same tissue has been reported to be similar.
Function
Biglycan is believed to play a role in the mineralisation of bone. Knock-out mice that have had the gene for biglycan suppressed have an osteoporosisOsteoporosis
Osteoporosis is a disease of bones that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is deteriorating, and the amount and variety of proteins in bone is altered...
-like phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
with reduced growth rate and lower bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
mass than mice that can express biglycan.
Biglycan core protein binds to the growth factors BMP-4 and influences its bioactivity. It has also been reported that the presence of biglycan is necessary for BMP-4 to exert its effects on osteoblasts. There is also evidence that biglycan binds to TGF-beta 1