Type-IV collagen
Type-IV collagen is a type of 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...

 found primarily in the basal lamina
Basal lamina
The basal lamina is a layer of extracellular matrix secreted by the epithelial cells, on which the epithelium sits. It is often confused with the basement membrane, and sometimes used inconsistently in the literature, see below....

. The type IV collagen C4 domain
Type IV collagen C4 domain
In molecular biology, the type IV collagen C4 domain is a duplicated domain present at the C-terminus of type IV collagens. Each type IV collagen contains a long triple-helical collagenous domain flanked by a short 7S domain of 25 amino acids and a globular non-collagenous C4 domain of ~230 amino...

 at the C-terminus is not removed in post-translational processing, and the fibers link head-to-head, rather than in parallel. Also, type-IV lacks the regular glycine
Glycine is an organic compound with the formula NH2CH2COOH. Having a hydrogen substituent as its 'side chain', glycine is the smallest of the 20 amino acids commonly found in proteins. Its codons are GGU, GGC, GGA, GGG cf. the genetic code.Glycine is a colourless, sweet-tasting crystalline solid...

 in every third residue necessary for the tight, collagen helix
Collagen helix
In collagen, the collagen helix, or type-2 helix, is a major shape in secondary structure. It consists of a triple helix made of the repetitious amino acid sequence glycine - X - Y, where X and Y are frequently proline or hydroxyproline....

. This makes the overall arrangement more sloppy with kinks. These two features cause the collagen to form in a sheet, the form of the basal lamina

There are six human genes associated with it:
  • COL4A1
    Collagen alpha-1 chain is a protein that in humans is encoded by the COL4A1 gene.Mutations in COL4A1 exons 24 and 25 are associated with HANAC ....

    , COL4A2
    Collagen alpha-2 chain is a protein that in humans is encoded by the COL4A2 gene.-Further reading:...

    , COL4A3
    Collagen alpha-3 chain is a protein that in humans is encoded by the COL4A3 gene.-Further reading:...

    , COL4A4
    Collagen alpha-4 chain is a protein that in humans is encoded by the COL4A4 gene.-Further reading:...

    , COL4A5
    Collagen alpha-5 chain is a protein that in humans is encoded by the COL4A5 gene.-Disease Database:-Further reading:...

    , COL4A6
    Collagen alpha-6 chain is a protein that in humans is encoded by the COL4A6 gene.-Further reading:...

Clinical significance

The alpha 3 protein constituent of type-IV collagen is thought to be the antigen implicated in Goodpasture's syndrome
Goodpasture's syndrome
Goodpasture’s syndrome is a rare disease characterized by glomerulonephritis and hemorrhaging of the lungs...

, wherein the immune system attacks the basement membrane
Basement membrane
The basement membrane is a thin sheet of fibers that underlies the epithelium, which lines the cavities and surfaces of organs including skin, or the endothelium, which lines the interior surface of blood vessels.- Composition :...

s of the glomeruli
A glomerulus is a capillary tuft that is involved in the first step of filtering blood to form urine.A glomerulus is surrounded by Bowman's capsule, the beginning component of nephrons in the vertebrate kidney. A glomerulus receives its blood supply from an afferent arteriole of the renal...

 and the alveoli.

Mutations to the genes coding for type-IV collagen lead to Alport syndrome
Alport syndrome
Alport syndrome or hereditary nephritis is a genetic disorder characterized by glomerulonephritis, endstage kidney disease, and hearing loss. Alport syndrome can also affect the eyes . The presence of blood in the urine is almost always found in this condition.It was first identified in a British...

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