procollagen

プロコラーゲン

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/10/30 10:23:15」(JST)

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Tropocollagen molecule: three left-handed procollagens (red, green, blue) join to form a right handed triple helical tropocollagen.

Collagen /ˈkɒlədʒᵻn/ is the main structural protein in the extracellular space in the various connective tissues in animal bodies. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole-body protein content. Depending upon the degree of mineralization, collagen tissues may be rigid (bone), compliant (tendon), or have a gradient from rigid to compliant (cartilage). Collagen, in the form of elongated fibrils, is mostly found in fibrous tissues such as tendons, ligaments and skin. It is also abundant in corneas, cartilage, bones, blood vessels, the gut, intervertebral discs and the dentin in teeth. In muscle tissue, it serves as a major component of the endomysium. Collagen constitutes one to two percent of muscle tissue, and accounts for 6% of the weight of strong, tendinous muscles. The fibroblast is the most common cell that creates collagen.

Gelatin, which is used in food and industry, is collagen that has been irreversibly hydrolyzed. Collagen also has many medical uses in treating complications of the bones and skin.

The name collagen comes from the Greek κόλλα (kólla), meaning "glue", and suffix -γέν, -gen, denoting "producing". This refers to the compound's early use in the process of boiling the skin and sinews of horses and other animals to obtain glue.

Types of collagen

Collagen occurs in many places throughout the body. Over 90% of the collagen in the human body, however, is type I.

So far, 28 types of collagen have been identified and described. They can be divided into several groups according to the structure they form:

• Fibrillar (Type I, II, III, V, XI)
• Non-fibrillar
  • FACIT (Fibril Associated Collagens with Interrupted Triple Helices) (Type IX, XII, XIV, XVI, XIX)
  • Short chain (Type VIII, X)
  • Basement membrane (Type IV)
  • Multiplexin (Multiple Triple Helix domains with Interruptions) (Type XV, XVIII)
  • MACIT (Membrane Associated Collagens with Interrupted Triple Helices) (Type XIII, XVII)
  • Other (Type VI, VII)

The five most common types are:

• Type I: skin, tendon, vascular ligature, organs, bone (main component of the organic part of bone)
• Type II: cartilage (main collagenous component of cartilage)
• Type III: reticulate (main component of reticular fibers), commonly found alongside type I.
• Type IV: forms basal lamina, the epithelium-secreted layer of the basement membrane.
• Type V: cell surfaces, hair and placenta

Medical uses

Cardiac applications

The collagenous cardiac skeleton which includes the four heart valve rings, is histologically, elastically and uniquely bound to cardiac muscle. The cardiac skeleton also includes the separating septa of the heart chambers – the interventricular septum and the atrioventricular septum. Collagen contribution to the measure of cardiac performance summarily represents a continuous torsional force opposed to the fluid mechanics of blood pressure emitted from the heart. The collagenous structure that divides the upper chambers of the heart from the lower chambers is an impermeable membrane that excludes both blood and electrical impulses through typical physiological means. With support from collagen, atrial fibrillation should never deteriorate to ventricular fibrillation. Collagen is layered in variable densities with cardiac muscle mass. The mass, distribution, age and density of collagen all contribute to the compliance required to move blood back and forth. Individual cardiac valvular leaflets are folded into shape by specialized collagen under variable pressure. Gradual calcium deposition within collagen occurs as a natural function of aging. Calcified points within collagen matrices show contrast in a moving display of blood and muscle, enabling methods of cardiac imaging technology to arrive at ratios essentially stating blood in (cardiac input) and blood out (cardiac output). Pathology of the collagen underpinning of the heart is understood within the category of connective tissue disease.

Cosmetic surgery

Collagen has been widely used in cosmetic surgery, as a healing aid for burn patients for reconstruction of bone and a wide variety of dental, orthopedic, and surgical purposes. Both human and bovine collagen is widely used as dermal fillers for treatment of wrinkles and skin aging. Some points of interest are:

1. When used cosmetically, there is a chance of allergic reactions causing prolonged redness; however, this can be virtually eliminated by simple and inconspicuous patch testing prior to cosmetic use.
2. Most medical collagen is derived from young beef cattle (bovine) from certified BSE-free animals. Most manufacturers use donor animals from either "closed herds", or from countries which have never had a reported case of BSE such as Australia, Brazil, and New Zealand.

Bone grafts

As the skeleton forms the structure of the body, it is vital that it maintains its strength, even after breaks and injuries. Collagen is used in bone grafting as it has a triple helical structure, making it a very strong molecule. It is ideal for use in bones, as it does not compromise the structural integrity of the skeleton. The triple helical structure of collagen prevents it from being broken down by enzymes, it enables adhesiveness of cells and it is important for the proper assembly of the extracellular matrix.

Tissue regeneration

Collagen scaffolds are used in tissue regeneration, whether in sponges, thin sheets, or gels. Collagen has the correct properties for tissue regeneration such as pore structure, permeability, hydrophilicity and it is stable in vivo. Collagen scaffolds are also ideal for the deposition of cells, such as osteoblasts and fibroblasts and once inserted, growth is able to continue as normal in the tissue.

Reconstructive surgical uses

Collagens are widely employed in the construction of the artificial skin substitutes used in the management of severe burns. These collagens may be derived from bovine, equine, porcine, or even human sources; and are sometimes used in combination with silicones, glycosaminoglycans, fibroblasts, growth factors and other substances.

Collagen is also sold commercially in pill form as a supplement to aid joint mobility. However, because proteins are broken down into amino acids before absorption, there is no reason for orally ingested collagen to affect connective tissue in the body, except through the effect of individual amino acid supplementation.

Collagen is also frequently used in scientific research applications for cell culture, studying cell behavior and cellular interactions with the extracellular environment.

Wound care

Collagen is one of the body’s key natural resources and a component of skin tissue that can benefit all stages of the wound healing process. When collagen is made available to the wound bed, closure can occur. Wound deterioration, followed sometimes by procedures such as amputation, can thus be avoided.

Collagen is a natural product, therefore it is used as a natural wound dressing and has properties that artificial wound dressings do not have. It is resistant against bacteria, which is of vital importance in a wound dressing. It helps to keep the wound sterile, because of its natural ability to fight infection. When collagen is used as a burn dressing, healthy granulation tissue is able to form very quickly over the burn, helping it to heal rapidly.

Throughout the 4 phases of wound healing, collagen performs the following functions in wound healing:

• Guiding function: Collagen fibers serve to guide fibroblasts. Fibroblasts migrate along a connective tissue matrix.
• Chemotactic properties: The large surface area available on collagen fibers can attract fibrogenic cells which help in healing.
• Nucleation: Collagen, in the presence of certain neutral salt molecules can act as a nucleating agent causing formation of fibrillar structures. A collagen wound dressing might serve as a guide for orienting new collagen deposition and capillary growth.
• Hemostatic properties: Blood platelets interact with the collagen to make a hemostatic plug.

Veterinary use

Some studies have shown efficacy of collagen supplementation for dogs with osteoarthritis pain, alone or in combination with other nutraceuticals like glucosamine and chondroitin.

Chemistry

The collagen protein is composed of a triple helix, which generally consists of two identical chains (α1) and an additional chain that differs slightly in its chemical composition (α2). The amino acid composition of collagen is atypical for proteins, particularly with respect to its high hydroxyproline content. The most common motifs in the amino acid sequence of collagen are glycine-proline-X and glycine-X-hydroxyproline, where X is any amino acid other than glycine, proline or hydroxyproline. The average amino acid composition for fish and mammal skin is given.

Amino acid	Abundance in mammal skin (residues/1000)	Abundance in fish skin (residues/1000)
Glycine	329	339
Proline	126	108
Alanine	109	114
Hydroxyproline	95	67
Glutamic acid	74	76
Arginine	49	52
Aspartic acid	47	47
Serine	36	46
Lysine	29	26
Leucine	24	23
Valine	22	21
Threonine	19	26
Phenylalanine	13	14
Isoleucine	11	11
Hydroxylysine	6	8
Methionine	6	13
Histidine	5	7
Tyrosine	3	3
Cysteine	1	1
Tryptophan	0	0

Synthesis

First, a three-dimensional stranded structure is assembled, with the amino acids glycine and proline as its principal components. This is not yet collagen but its precursor, procollagen. Procollagen is then modified by the addition of hydroxyl groups to the amino acids proline and lysine. This step is important for later glycosylation and the formation of the triple helix structure of collagen. The hydroxylase enzymes that perform these reactions require Vitamin C as a cofactor, and a deficiency in this vitamin results in impaired collagen synthesis and the resulting disease scurvy These hydroxylation reactions are catalyzed by two different enzymes: prolyl-4-hydroxylase and lysyl-hydroxylase. Vitamin C also serves with them in inducing these reactions. In this service, one molecule of vitamin C is destroyed for each H replaced by OH. The synthesis of collagen occurs inside and outside of the cell. The formation of collagen which results in fibrillary collagen (most common form) is discussed here. Meshwork collagen, which is often involved in the formation of filtration systems, is the other form of collagen. All types of collagens are triple helices, and the differences lie in the make-up of the alpha peptides created in step 2.

1. Transcription of mRNA: About 34 genes are associated with collagen formation, each coding for a specific mRNA sequence, and typically have the "COL" prefix. The beginning of collagen synthesis begins with turning on genes which are associated with the formation of a particular alpha peptide (typically alpha 1, 2 or 3).
2. Pre-pro-peptide formation: Once the final mRNA exits from the cell nucleus and enters into the cytoplasm, it links with the ribosomal subunits and the process of translation occurs. The early/first part of the new peptide is known as the signal sequence. The signal sequence on the N-terminal of the peptide is recognized by a signal recognition particle on the endoplasmic reticulum, which will be responsible for directing the pre-pro-peptide into the endoplasmic reticulum. Therefore, once the synthesis of new peptide is finished, it goes directly into the endoplasmic reticulum for post-translational processing. It is now known as pre-pro-collagen.
3. Pre-pro-peptide to pro-collagen: Three modifications of the pre-pro-peptide occur leading to the formation of the alpha peptide:
   1. The signal peptide on the N-terminal is dissolved, and the molecule is now known as propeptide (not procollagen).
   2. Hydroxylation of lysines and prolines on propeptide by the enzymes 'prolyl hydroxylase' and 'lysyl hydroxylase' (to produce hydroxyproline and hydroxylysine) occurs to aid cross-linking of the alpha peptides. This enzymatic step requires vitamin C as a cofactor. In scurvy, the lack of hydroxylation of prolines and lysines causes a looser triple helix (which is formed by three alpha peptides).
   3. Glycosylation occurs by adding either glucose or galactose monomers onto the hydroxyl groups that were placed onto lysines, but not on prolines.
   4. Once these modifications have taken place, three of the hydroxylated and glycosylated propeptides twist into a triple helix forming procollagen. Procollagen still has unwound ends, which will be later trimmed. At this point, the procollagen is packaged into a transfer vesicle destined for the Golgi apparatus.
4. Golgi apparatus modification: In the Golgi apparatus, the procollagen goes through one last post-translational modification before being secreted out of the cell. In this step, oligosaccharides (not monosaccharides as in step 3) are added, and then the procollagen is packaged into a secretory vesicle destined for the extracellular space.
5. Formation of tropocollagen: Once outside the cell, membrane bound enzymes known as 'collagen peptidases', remove the "loose ends" of the procollagen molecule. What is left is known as tropocollagen. Defects in this step produce one of the many collagenopathies known as Ehlers-Danlos syndrome. This step is absent when synthesizing type III, a type of fibrilar collagen.
6. Formation of the collagen fibril: 'Lysyl oxidase', an extracellular enzyme, produces the final step in the collagen synthesis pathway. This enzyme acts on lysines and hydroxylysines producing aldehyde groups, which will eventually undergo covalent bonding between tropocollagen molecules. This polymer of tropocollogen is known as a collagen fibril.

Action of lysyl oxidase

Amino acids

Collagen has an unusual amino acid composition and sequence:

• Glycine is found at almost every third residue.
• Proline makes up about 17% of collagen.
• Collagen contains two uncommon derivative amino acids not directly inserted during translation. These amino acids are found at specific locations relative to glycine and are modified post-translationally by different enzymes, both of which require vitamin C as a cofactor.
  • Hydroxyproline derived from proline
  • Hydroxylysine derived from lysine - depending on the type of collagen, varying numbers of hydroxylysines are glycosylated (mostly having disaccharides attached).

Cortisol stimulates degradation of (skin) collagen into amino acids.

Collagen I formation

Most collagen forms in a similar manner, but the following process is typical for type I:

1. Inside the cell
   1. Two types of alpha chains are formed during translation on ribosomes along the rough endoplasmic reticulum (RER): alpha-1 and alpha-2 chains. These peptide chains (known as preprocollagen) have registration peptides on each end and a signal peptide.
   2. Polypeptide chains are released into the lumen of the RER.
   3. Signal peptides are cleaved inside the RER and the chains are now known as pro-alpha chains.
   4. Hydroxylation of lysine and proline amino acids occurs inside the lumen. This process is dependent on ascorbic acid (vitamin C) as a cofactor.
   5. Glycosylation of specific hydroxylysine residues occurs.
   6. Triple alpha helical structure is formed inside the endoplasmic reticulum from two alpha-1 chains and one alpha-2 chain.
   7. Procollagen is shipped to the Golgi apparatus, where it is packaged and secreted by exocytosis.
2. Outside the cell
   1. Registration peptides are cleaved and tropocollagen is formed by procollagen peptidase.
   2. Multiple tropocollagen molecules form collagen fibrils, via covalent cross-linking (aldol reaction) by lysyl oxidase which links hydroxylysine and lysine residues. Multiple collagen fibrils form into collagen fibers.
   3. Collagen may be attached to cell membranes via several types of protein, including fibronectin and integrin.

Synthetic pathogenesis

Vitamin C deficiency causes scurvy, a serious and painful disease in which defective collagen prevents the formation of strong connective tissue. Gums deteriorate and bleed, with loss of teeth; skin discolors, and wounds do not heal. Prior to the 18th century, this condition was notorious among long-duration military, particularly naval, expeditions during which participants were deprived of foods containing vitamin C.

An autoimmune disease such as lupus erythematosus or rheumatoid arthritis may attack healthy collagen fibers.

Many bacteria and viruses secrete virulence factors, such as the enzyme collagenase, which destroys collagen or interferes with its production.

Molecular structure

A single collagen molecule, tropocollagen, is used to make up larger collagen aggregates, such as fibrils. It is approximately 300 nm long and 1.5 nm in diameter, and it is made up of three polypeptide strands (called alpha peptides, see step 2), each of which has the conformation of a left-handed helix – this should not be confused with the right-handed alpha helix. These three left-handed helices are twisted together into a right-handed triple helix or "super helix", a cooperative quaternary structure stabilized by many hydrogen bonds. With type I collagen and possibly all fibrillar collagens, if not all collagens, each triple-helix associates into a right-handed super-super-coil referred to as the collagen microfibril. Each microfibril is interdigitated with its neighboring microfibrils to a degree that might suggest they are individually unstable, although within collagen fibrils, they are so well ordered as to be crystalline.

Three polypeptides coil to form tropocollagen. Many tropocollagens then bind together to form a fibril, and many of these then form a fibre.

A distinctive feature of collagen is the regular arrangement of amino acids in each of the three chains of these collagen subunits. The sequence often follows the pattern Gly-Pro-X or Gly-X-Hyp, where X may be any of various other amino acid residues. Proline or hydroxyproline constitute about 1/6 of the total sequence. With glycine accounting for the 1/3 of the sequence, this means approximately half of the collagen sequence is not glycine, proline or hydroxyproline, a fact often missed due to the distraction of the unusual GX₁X₂ character of collagen alpha-peptides. The high glycine content of collagen is important with respect to stabilization of the collagen helix as this allows the very close association of the collagen fibers within the molecule, facilitating hydrogen bonding and the formation of intermolecular cross-links. This kind of regular repetition and high glycine content is found in only a few other fibrous proteins, such as silk fibroin.

Collagen is not only a structural protein. Due to its key role in the determination of cell phenotype, cell adhesion, tissue regulation and infrastructure, many sections of its non-proline-rich regions have cell or matrix association / regulation roles. The relatively high content of proline and hydroxyproline rings, with their geometrically constrained carboxyl and (secondary) amino groups, along with the rich abundance of glycine, accounts for the tendency of the individual polypeptide strands to form left-handed helices spontaneously, without any intrachain hydrogen bonding.

Because glycine is the smallest amino acid with no side chain, it plays a unique role in fibrous structural proteins. In collagen, Gly is required at every third position because the assembly of the triple helix puts this residue at the interior (axis) of the helix, where there is no space for a larger side group than glycine’s single hydrogen atom. For the same reason, the rings of the Pro and Hyp must point outward. These two amino acids help stabilize the triple helix—Hyp even more so than Pro; a lower concentration of them is required in animals such as fish, whose body temperatures are lower than most warm-blooded animals. Lower proline and hydroxyproline contents are characteristic of cold-water, but not warm-water fish; the latter tend to have similar proline and hydroxyproline contents to mammals. The lower proline and hydroxproline contents of cold-water fish and other poikilotherm animals leads to their collagen having a lower thermal stability than mammalian collagen. This lower thermal stability means that gelatin derived from fish collagen is not suitable for many food and industrial applications.

The tropocollagen subunits spontaneously self-assemble, with regularly staggered ends, into even larger arrays in the extracellular spaces of tissues. Additional assembly of fibrils is guided by fibroblasts, which deposit fully formed fibrils from fibripositors. In the fibrillar collagens, the molecules are staggered from each other by about 67 nm (a unit that is referred to as ‘D’ and changes depending upon the hydration state of the aggregate). Each D-period contains four plus a fraction collagen molecules, because 300 nm divided by 67 nm does not give an integer (the length of the collagen molecule divided by the stagger distance D). Therefore, in each D-period repeat of the microfibril, there is a part containing five molecules in cross-section, called the “overlap”, and a part containing only four molecules, called the "gap". The triple-helices are also arranged in a hexagonal or quasihexagonal array in cross-section, in both the gap and overlap regions.

There is some covalent crosslinking within the triple helices, and a variable amount of covalent crosslinking between tropocollagen helices forming well organized aggregates (such as fibrils). Larger fibrillar bundles are formed with the aid of several different classes of proteins (including different collagen types), glycoproteins and proteoglycans to form the different types of mature tissues from alternate combinations of the same key players. Collagen's insolubility was a barrier to the study of monomeric collagen until it was found that tropocollagen from young animals can be extracted because it is not yet fully crosslinked. However, advances in microscopy techniques (i.e. electron microscopy (EM) and atomic force microscopy (AFM)) and X-ray diffraction have enabled researchers to obtain increasingly detailed images of collagen structure in situ. These later advances are particularly important to better understanding the way in which collagen structure affects cell–cell and cell–matrix communication, and how tissues are constructed in growth and repair, and changed in development and disease. For example, using AFM–based nanoindentation it has been shown that a single collagen fibril is a heterogeneous material along its axial direction with significantly different mechanical properties in its gap and overlap regions, correlating with its different molecular organizations in these two regions.

Collagen fibrils/aggregates are arranged in different combinations and concentrations in various tissues to provide varying tissue properties. In bone, entire collagen triple helices lie in a parallel, staggered array. 40 nm gaps between the ends of the tropocollagen subunits (approximately equal to the gap region) probably serve as nucleation sites for the deposition of long, hard, fine crystals of the mineral component, which is (approximately) Ca₁₀(OH)₂(PO₄)₆. Type I collagen gives bone its tensile strength.

Associated disorders

Collagen-related diseases most commonly arise from genetic defects or nutritional deficiencies that affect the biosynthesis, assembly, postranslational modification, secretion, or other processes involved in normal collagen production.

Genetic Defects of Collagen Genes

Type	Notes	Gene(s)	Disorders
I	This is the most abundant collagen of the human body. It is present in scar tissue, the end product when tissue heals by repair. It is found in tendons, skin, artery walls, cornea, the endomysium surrounding muscle fibers, fibrocartilage, and the organic part of bones and teeth.	COL1A1, COL1A2	Osteogenesis imperfecta, Ehlers–Danlos syndrome, Infantile cortical hyperostosis a.k.a. Caffey's disease
II	Hyaline cartilage, makes up 50% of all cartilage protein. Vitreous humour of the eye.	COL2A1	Collagenopathy, types II and XI
III	This is the collagen of granulation tissue, and is produced quickly by young fibroblasts before the tougher type I collagen is synthesized. Reticular fiber. Also found in artery walls, skin, intestines and the uterus	COL3A1	Ehlers–Danlos syndrome, Dupuytren's contracture
IV	Basal lamina; eye lens. Also serves as part of the filtration system in capillaries and the glomeruli of nephron in the kidney.	COL4A1, COL4A2, COL4A3, COL4A4, COL4A5, COL4A6	Alport syndrome, Goodpasture's syndrome
V	Most interstitial tissue, assoc. with type I, associated with placenta	COL5A1, COL5A2, COL5A3	Ehlers–Danlos syndrome (Classical)
VI	Most interstitial tissue, assoc. with type I	COL6A1, COL6A2, COL6A3, COL6A5	Ulrich myopathy, Bethlem myopathy, Atopic dermatitis
VII	Forms anchoring fibrils in dermoepidermal junctions	COL7A1	Epidermolysis bullosa dystrophica
VIII	Some endothelial cells	COL8A1, COL8A2	Posterior polymorphous corneal dystrophy 2
IX	FACIT collagen, cartilage, assoc. with type II and XI fibrils	COL9A1, COL9A2, COL9A3	EDM2 and EDM3
X	Hypertrophic and mineralizing cartilage	COL10A1	Schmid metaphyseal dysplasia
XI	Cartilage	COL11A1, COL11A2	Collagenopathy, types II and XI
XII	FACIT collagen, interacts with type I containing fibrils, decorin and glycosaminoglycans	COL12A1	–
XIII	Transmembrane collagen, interacts with integrin a1b1, fibronectin and components of basement membranes like nidogen and perlecan.	COL13A1	–
XIV	FACIT collagen, also known as undulin	COL14A1	–
XV	–	COL15A1	–
XVI	–	COL16A1	–
XVII	Transmembrane collagen, also known as BP180, a 180 kDa protein	COL17A1	Bullous pemphigoid and certain forms of junctional epidermolysis bullosa
XVIII	Source of endostatin	COL18A1	–
XIX	FACIT collagen	COL19A1	–
XX	–	COL20A1	–
XXI	FACIT collagen	COL21A1	–
XXII	–	COL22A1	–
XXIII	MACIT collagen	COL23A1	–
XXIV	–	COL24A1	–
XXV	–	COL25A1	–
XXVI	–	EMID2	–
XXVII	–	COL27A1	–
XXVIII	–	COL28A1	–

In addition to the above-mentioned disorders, excessive deposition of collagen occurs in scleroderma.

Diseases

One thousand mutations have been identified in twelve out of more than twenty types of collagen. These mutations can lead to various diseases at the tissue level.

Osteogenesis imperfecta – Caused by a mutation in type 1 collagen, dominant autosomal disorder, results in weak bones and irregular connective tissue, some cases can be mild while others can be lethal, mild cases have lowered levels of collagen type 1 while severe cases have structural defects in collagen.

Chondrodysplasias – Skeletal disorder believed to be caused by a mutation in type 2 collagen, further research is being conducted to confirm this.

Ehlers-Danlos Syndrome – Six different types of this disorder, which lead to deformities in connective tissue. Some types can be lethal, leading to the rupture of arteries. Each syndrome is caused by a different mutation, for example type four of this disorder is caused by a mutation in collagen type 3.

Alport syndrome – Can be passed on genetically, usually as X-linked dominant, but also as both an autosomal dominant and autosomal recessive disorder, sufferers have problems with their kidneys and eyes, loss of hearing can also develop in during the childhood or adolescent years.

Osteoporosis – Not inherited genetically, brought on with age, associated with reduced levels of collagen in the skin and bones, growth hormone injections are being researched as a possible treatment to counteract any loss of collagen.

Knobloch syndrome – Caused by a mutation in the COL18A1 gene that codes for the production of collagen XVIII. Patients present with protrusion of the brain tissue and degeneration of the retina, an individual who has family members suffering from the disorder are at an increased risk of developing it themselves as there is a hereditary link.

Characteristics

Collagen is one of the long, fibrous structural proteins whose functions are quite different from those of globular proteins, such as enzymes. Tough bundles of collagen called collagen fibers are a major component of the extracellular matrix that supports most tissues and gives cells structure from the outside, but collagen is also found inside certain cells. Collagen has great tensile strength, and is the main component of fascia, cartilage, ligaments, tendons, bone and skin. Along with elastin and soft keratin, it is responsible for skin strength and elasticity, and its degradation leads to wrinkles that accompany aging. It strengthens blood vessels and plays a role in tissue development. It is present in the cornea and lens of the eye in crystalline form. It may be one of the most abundant proteins in the fossil record, given that it appears to fossilize frequently, even in bones from the Mesozoic and Paleozoic.

Uses

Collagen has a wide variety of applications, from food to medical. For instance, it is used in cosmetic surgery and burn surgery. It is widely used in the form of collagen casings for sausages, which are also used in the manufacture of musical strings.

If collagen is subject to sufficient denaturation, e.g. by heating, the three tropocollagen strands separate partially or completely into globular domains, containing a different secondary structure to the normal collagen polyproline II (PPII), e.g. random coils. This process describes the formation of gelatin, which is used in many foods, including flavored gelatin desserts. Besides food, gelatin has been used in pharmaceutical, cosmetic, and photography industries.

From the Greek for glue, kolla, the word collagen means "glue producer" and refers to the early process of boiling the skin and sinews of horses and other animals to obtain glue. Collagen adhesive was used by Egyptians about 4,000 years ago, and Native Americans used it in bows about 1,500 years ago. The oldest glue in the world, carbon-dated as more than 8,000 years old, was found to be collagen—used as a protective lining on rope baskets and embroidered fabrics, and to hold utensils together; also in crisscross decorations on human skulls. Collagen normally converts to gelatin, but survived due to dry conditions. Animal glues are thermoplastic, softening again upon reheating, and so they are still used in making musical instruments such as fine violins and guitars, which may have to be reopened for repairs—an application incompatible with tough, synthetic plastic adhesives, which are permanent. Animal sinews and skins, including leather, have been used to make useful articles for millennia.

Gelatin-resorcinol-formaldehyde glue (and with formaldehyde replaced by less-toxic pentanedial and ethanedial) has been used to repair experimental incisions in rabbit lungs.

History

The molecular and packing structures of collagen have eluded scientists over decades of research. The first evidence that it possesses a regular structure at the molecular level was presented in the mid-1930s. Since that time, many prominent scholars, including Nobel laureates Crick, Pauling, Rich and Yonath, and others, including Brodsky, Berman, and Ramachandran, concentrated on the conformation of the collagen monomer. Several competing models, although correctly dealing with the conformation of each individual peptide chain, gave way to the triple-helical "Madras" model of Ramachandran, which provided an essentially correct model of the molecule's quaternary structure although this model still required some refinement. The packing structure of collagen has not been defined to the same degree outside of the fibrillar collagen types, although it has been long known to be hexagonal or quasi-hexagonal. As with its monomeric structure, several conflicting models alleged that either the packing arrangement of collagen molecules is 'sheet-like' or microfibrillar. The microfibrillar structure of collagen fibrils in tendon, cornea and cartilage has been directly imaged by electron microscopy. The microfibrillar structure of tail tendon, as described by Fraser, Miller, and Wess (amongst others), was modeled as being closest to the observed structure, although it oversimplified the topological progression of neighboring collagen molecules, and hence did not predict the correct conformation of the discontinuous D-periodic pentameric arrangement termed simply: the microfibril. Various cross linking agents like L-Dopaquinone, embeline, potassium embelate and 5-O-methyl embelin could be developed as potential cross-linking/stabilization agents of collagen preparation and its application as wound dressing sheet in clinical applications is enhanced.

See also

• Hydrolyzed collagen, a common form in which collagen is sold as a supplement.
• Animal glue
• Gelatine
• Fibrous protein
• Osteoid, collagen containing component of bone
• Lysyl oxidase and LOXL1, LOXL2, LOXL3, LOXL4 in collagen formation
• Collagenase, the enzyme involved in collagen breakdown and remodelling. For more on other proteases that target collagen see The Proteolysis Map
• Ehlers-Danlos Syndrome
• Hypermobility Syndrome
• Sponge - Cell types
• Drug discovery and development of MMP inhibitors

References

External links

• 12 types of collagen
• Database of type I and type III collagen mutations
• Science.dirbix Collagen
• Collagen Stability Calculator
• Computer-generated animations of the assembly of Type I and Type IV Collagens
• Integrin-Collagen interface, PMAP (The Proteolysis Map)—animation
• Integrin-Collagen binding model, PMAP (The Proteolysis Map)—animation
• Collagen-Integrin atomic detail, PMAP (The Proteolysis Map)—animation
• Saad M. (1994) "Low resolution structure and packing investigations of collagen crystalline domains in tendon using Synchrotron Radiation X-rays, Structure factors determination, evaluation of Isomorphous Replacement methods and other modeling." PhD Thesis, Université Joseph Fourier Grenoble 1

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English Journal

• TBS reflects trabecular microarchitecture in premenopausal women and men with idiopathic osteoporosis and low-traumatic fractures.

• Muschitz C1, Kocijan R2, Haschka J2, Pahr D3, Kaider A4, Pietschmann P5, Hans D6, Muschitz GK7, Fahrleitner-Pammer A8, Resch H2.
• Bone.Bone.2015 Oct;79:259-66. doi: 10.1016/j.bone.2015.06.007. Epub 2015 Jun 16.
• Transiliac bone biopsies, while widely considered to be the standard for the analysis of bone microstructure, are typically restricted to specialized centers. The benefit of Trabecular Bone Score (TBS) in addition to areal bone mineral density (aBMD) for fracture risk assessment has been documented
• PMID 26092650

• The active role of osteoporosis in the interaction between osteoblasts and bone metastases.

• Pagani S1, Fini M2, Giavaresi G2, Salamanna F3, Borsari V3.
• Bone.Bone.2015 Oct;79:176-82. doi: 10.1016/j.bone.2015.06.002. Epub 2015 Jun 6.
• INTRODUCTION: To minimize the severity of bone metastases and to delay their onset, it is important to analyze the underlying biological mechanisms. The present study focused on the link between OP and metastatic cells, with particular attention to osteoblast behavior.METHODS: Osteoblasts (OB) were
• PMID 26057367

• Ascorbyl coumarates as multifunctional cosmeceutical agents that inhibit melanogenesis and enhance collagen synthesis.

• Kwak JY1, Park S, Seok JK, Liu KH, Boo YC.
• Archives of dermatological research.Arch Dermatol Res.2015 Sep;307(7):635-43. doi: 10.1007/s00403-015-1583-x. Epub 2015 Jun 16.
• L-Ascorbic acid (AA) and p-coumaric acid (p-CA) are naturally occurring antioxidants that are known to enhance collagen synthesis and inhibit melanin synthesis, respectively. The purpose of this study was to examine hybrid compounds between AA and p-CA as multifunctional cosmeceutical agents. Ascorb
• PMID 26078014

Japanese Journal

• Liver elasticity measurement before and after biliary drainage in patients with obstructive jaundice : a prospective cohort studya prospective cohort study

• BMC gastroenterology 16, 65, 2016-07-08
• NAID 120005828467

• 歯肉溝滲出液中のバイオマーカーを用いた歯周病診断

• Journal of Oral Health and Biosciences 29(1), 13-20, 2016-06-30
• NAID 120005823530

• 関節リウマチ患者の骨粗鬆症に対するデノスマブ１年間の治療効果

• 臨床リウマチ 28(1), 46-52, 2016
• NAID 130005154618

Related Links

• Procollagen | definition of procollagen by Medical dictionary

pro·col·la·gen (prō-kol'ă-jen), Soluble precursor of tropocollagen formed by fibroblasts and other cells in the process of collagen synthesis; unstable type III procollagen is associated with Ehlers-Danlos syndrome type IV. procollagen ...

• Anti-Human Procollagen Type I C-peptide (PIP)｜タカラバイオ ...

メーカー 略称 製品コード TaKaRa Code 製品名 容量 価格（税別） 特記事項 説明書 データシート ベクター情報 参考 資料 TKR M011 M011 Anti-Human Procollagen Type I C-peptide (PIP), Monoclonal (Clone PC5-5) 0.1 mg ￥55,000 TKR

Related Pictures

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★リンクテーブル★

リンク元	「コラーゲン」「プロコラーゲン」
拡張検索	「procollagen peptidase」「procollagen-proline dioxygenase」「type III procollagen-N-peptide」

「コラーゲン」

　　[★]

英

collagen

同

膠原

関

• first aid step1 2006 p.85,86,114,288,291,292,301,306,319,321,385,427

遺伝子

• COL1A1 17q22
• COL1A2 7q22.1
• COL2A1 12q13
• COL11A2 6p21.3

これらの遺伝子の変異による結合組織疾患はdominant negative mutationである。

臨床関連

• 骨形成不全

コラーゲンの種類

• HIS.97 NDE.5

	場所
I型コラーゲン	狭義の結合組織、骨、歯の象牙質とセメント質に存在
II型コラーゲン	硝子軟骨、弾性軟骨
III型コラーゲン	細網線維
IV型コラーゲン	基底板の緻密板を作る
V型コラーゲン	I型コラーゲンと関連。胎盤に存在
VII型コラーゲン	基底板を細網線維に付着。anchoring fibril
XVII型コラーゲン	ヘミデスモソームと基底板を連結

生合成

• first aid step1 2006 p.85
• ER：ER内でOH化(Pro, Lys)：preprocollagen
• Golgi：Lysの糖鎖付加：procollagen(triple helix of 3 collagen α chains)
• EM：procollagen　－procollagen peptidase→　tropocollagen
• ：tropocollagen　－covalent lysine-hydroxylysine cross-linkage by lysyl oxidase　→　collagen fibrils

「プロコラーゲン」

　　[★]

英

procollagen

関

プロコラーゲンIIIペプチド

「procollagen peptidase」

　　[★]

プロコラーゲンペプチダーゼ

関

procollagen N-endopeptidase、procollagen N-proteinase

「procollagen-proline dioxygenase」

　　[★]

プロコラーゲン・プロリンジオキシゲナーゼ

「type III procollagen-N-peptide」

　　[★] III型プロコラーゲンN末端ペプチド