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They bridge a 2-4 nm gap between cell membranes. [3] Gap junctions use protein complexes known as connexons to connect one cell to another. The proteins are called connexins. Gap junction proteins include the more than 26 types of connexin, and at least 12 non-connexin components that make up the gap junction complex or nexus. [4]
Gap junctions are collections of intercellular channels that allow ions and other tiny molecules to move directly between cells. [1] [14] These junctions are made up of a number of gap junction channels that consist of two connexons, each with six protein subunits called connexin, and a gene family of nearly 20 members encodes the connexins found in mammals [14] [15]
Connexins are commonly named according to their molecular weights, e.g. Cx26 is the connexin protein of 26 kDa. A competing nomenclature is the gap junction protein system, where connexins are sorted by their α (GJA) and β (GJB) forms, with additional connexins grouped into the C, D and E groupings, followed by an identifying number, e.g. GJA1 corresponds to Cx43.
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. [a] [5] Gap junction beta-1 protein is a member of the gap junction connexin family of proteins that regulates and controls the transfer of communication signals across cell membranes, primarily in the liver and peripheral nervous system. [6]
Gap junctions are the main site of cell-cell signaling or communication that allow small molecules to diffuse between adjacent cells. In vertebrates, gap junctions are composed of transmembrane proteins called connexins. They form hexagonal pores or channels through which ions, sugars, and other small molecules can pass.
Gap junctions play vital roles in the human body, [11] including their role in the uniform contractile of the heart muscle. [11] They are also relevant in signal transfers in the brain, and their absence shows a decreased cell density in the brain. [12] Retinal and skin cells are also dependent on gap junctions in cell differentiation and ...
Phosphorylation of gap junctions and their subunits is typically achieved through protein kinases, enzymes that add phosphates to the amino acids of proteins. [ 11 ] [ 12 ] [ 13 ] Serine/threonine kinases , which phosphorylate the hydroxyl group of serine or threonine residues, form the bulk of the Connexin phosphorylation kinases.
This gene encodes a gap junction protein. The encoded protein is known as a connexin, most of which form gap junctions that provide direct connections between neighboring cells. [5] However, Cx29, which is highly expressed in myelin-forming glial cells of the CNS and PNS, has not been documented to form gap junctions in any cell type.