Cochlin is a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
that in humans is encoded by the ''COCH''
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
.
It is an extracellular matrix (ECM) protein highly abundant in the cochlea and vestibule of the inner ear, constituting the major non-collagen component of the ECM of the inner ear.
The protein is highly conserved in human, mouse, and chicken, showing 94% and 79% amino acid identity of human to mouse and chicken sequences, respectively.
Structure
Cochlin contains three protein domains: an N-terminal
LCCL domain
In molecular biology, the LCCL domain is a protein domain which has been named after several well-characterised proteins that were found to contain it, namely Limulus clotting factor C, Cochlin (Coch-5b2) and Lgl1 ( CRISPLD2). It is an about 100 a ...
, and two copies of
Von Willebrand factor type A domain
The von Willebrand factor type A (vWA) domain is a protein domain named after its occurrence in von Willebrand factor (vWF), a large multimeric glycoprotein found in blood plasma. Mutant forms of vWF are involved in the aetiology of bleeding disor ...
s.
Function
The gene is expressed in spindle-shaped cells located along nerve fibers between the auditory ganglion and sensory epithelium. These cells accompany
neurite
A neurite or neuronal process refers to any projection from the cell body of a neuron. This projection can be either an axon or a dendrite. The term is frequently used when speaking of immature or developing neurons, especially of cells in culture ...
s at the
habenula perforata
In neuroanatomy, habenula (diminutive of Latin ''habena'' meaning rein) originally denoted the stalk of the pineal gland (pineal habenula; pedunculus of pineal body), but gradually came to refer to a neighboring group of nerve cells with which the ...
, the opening through which neurites extend to innervate hair cells. This and the pattern of expression of this gene in chicken inner ear paralleled the histologic findings of
acidophilic
Acidophiles or acidophilic organisms are those that thrive under highly acidic conditions (usually at pH 5.0 or below). These organisms can be found in different branches of the tree of life, including Archaea, Bacteria,Becker, A.Types of Bacteria ...
deposits, consistent with
mucopolysaccharide ground substance, in temporal bones from
DFNA9 (autosomal dominant nonsyndromic sensorineural deafness 9) patients. Mutations that cause DFNA9 have been reported in this gene.
Cochlin has been identified in the
trabecular meshwork (TM) of
glaucoma
Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...
patients, but not in healthy controls. The TM is a filter like area of tissue in the eye; cochlin may have a role in cell adhesion, mechanosensation, and modulation of the TM filter.
It is also expressed in
follicular dendritic cells in spleen and
lymph node
A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that inclu ...
s. Here, cochlin is cleaved by
aggrecanase
Aggrecanases are extracellular proteolytic enzymes that are members of the ADAMTS (A Disintegrin And Metalloprotease with Thrombospondin Motifs) family. Aggrecanases act on large proteoglycans known as aggrecans, which are components of connective ...
s and secreted into blood circulation during inflammation, contributing to the antibacterial
innate immune response
The innate, or nonspecific, immune system is one of the two main immunity strategies (the other being the adaptive immune system) in vertebrates. The innate immune system is an older evolutionary defense strategy, relatively speaking, and is the ...
.
References
Further reading
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{{InterPro content, IPR030743
Extracellular matrix proteins