Gap junction beta-2 protein (GJB2), also known as

connexin Connexins (Cx)TC# 1.A.24, or gap junction proteins, are structurally related transmembrane proteins that assemble to form vertebrate gap junctions. An entirely different family of proteins, the innexins, form gap junctions in invertebrates. Ea ...

26 (Cx26) — 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 ''GJB2''

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 ...

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 written ...

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 nucleobases 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 is called ...

from a string of six, resulting in a

frameshift Ribosomal frameshifting, also known as translational frameshifting or translational recoding, is a biological phenomenon that occurs during translation that results in the production of multiple, unique proteins from a single mRNA. The process can ...

and termination of the protein at

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

number 13. Having two copies of this mutation results in deafness. Connexin 26 also plays a role in

tumor suppression A tumor suppressor gene (TSG), or anti-oncogene, is a gene that regulates a cell during cell division and replication. If the cell grows uncontrollably, it will result in cancer. When a tumor suppressor gene is mutated, it results in a loss or red ...

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. Poss ...

, 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 Cancer stem cells (CSCs) are cancer cells (found within tumors or hematological cancers) that possess characteristics associated with normal stem cells, specifically the ability to give rise to all cell types found in a particular cancer sampl ...

Function

Gap junction Gap junctions are specialized intercellular connections between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulate ...

s were first characterized by

electron microscopy An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...

as regionally specialized structures on

plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

s of contacting adherent cells. These structures were shown to consist of cell-to-cell channels. Proteins, called

s, 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 Gap junction beta-1 protein (GJB1), also known as connexin 32 (Cx32) is a transmembrane protein that in humans is encoded by the ''GJB1'' gene. Gap junction beta-1 protein is a member of the gap junction connexin family of proteins that regulates ...

(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.

Clinical significance

Function

See also

References

Further reading