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Gap junction beta-2 protein (GJB2), also known as connexin 26 (Cx26) — is a
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
that in humans is encoded by the ''GJB2''
gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
.


Function

Gap junction Gap junctions are membrane channels between adjacent cells that allow the direct exchange of cytoplasmic substances, such small molecules, substrates, and metabolites. Gap junctions were first described as ''close appositions'' alongside tight ...
s were first characterized by electron microscopy as regionally specialized structures on
plasma membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...
s of contacting adherent cells. These structures were shown to consist of cell-to-cell channels. Proteins, called connexins, purified from fractions of enriched gap junctions from different tissues differ. The connexins are designated by their molecular mass. Another system of nomenclature divides gap junction proteins into two categories, alpha and beta, according to sequence similarities at the nucleotide and amino acid levels. For example, CX43 ( GJA1) is designated alpha-1 gap junction protein, whereas GJB1 (CX32), and GJB2 (CX26; this protein) are called beta-1 and beta-2 gap junction proteins, respectively. This nomenclature emphasizes that GJB1 and GJB2 are more homologous to each other than either of them is to gap junction protein, alpha GJA1. Gap junction beta-2 protein is a member of the connexin protein family and plays a crucial role in forming gap junctions, which are channels that allow the transport of nutrients, ions, and signaling molecules between adjacent cells. GJB2 is widely expressed throughout the body, with particularly important functions in the inner ear and skin. In the cochlea, GJB2 is believed to be essential for maintaining proper potassium ion levels and for the maturation of certain cochlear cells, both of which are critical for the process of converting sound waves into electrical nerve impulses. In the skin, GJB2 contributes to the growth, maturation, and stability of the epidermis.


Clinical significance

Defects in this gene lead to the most common form of congenital
deafness Deafness has varying definitions in cultural and medical contexts. In medical contexts, the meaning of deafness is hearing loss that precludes a person from understanding spoken language, an audiological condition. In this context it is writte ...
in developed countries, called DFNB1 (also known as connexin 26 deafness or ''GJB2''-related deafness). One fairly common mutation is the deletion of one
guanine Guanine () (symbol G or Gua) is one of the four main nucleotide bases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine ( uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside ...
from a string of six, resulting in a frameshift and termination of the protein at
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...
number 13. Having two copies of this mutation results in deafness. Connexin 26 also plays a role in tumor suppression through mediation of the cell cycle. The abnormal expression of Cx26, correlated with several types of human
cancers Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...
, may serve as a prognostic factor for cancers such as colorectal cancer, breast cancer, and bladder cancer. Furthermore, Cx26 over-expression is suggested to promote cancer development by facilitating cell migration and invasion and by stimulating the self-perpetuation ability of cancer stem cells.


See also

* Connexin *
Gap junction Gap junctions are membrane channels between adjacent cells that allow the direct exchange of cytoplasmic substances, such small molecules, substrates, and metabolites. Gap junctions were first described as ''close appositions'' alongside tight ...
* Vohwinkel syndrome * Bart–Pumphrey syndrome


References


Further reading

* * * * * * * * * {{gene-13-stub Connexins