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Gap junctions were first described as close appositions as other tight junctions, but following electron microscopy studies in 1967, they were renamed gap junctions to distinguish them from tight junctions. [2] They bridge a 2-4 nm gap between cell membranes. [3] Gap junctions use protein complexes known as connexons to
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 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]
Each gap junction (sometimes called a nexus) contains numerous gap junction channels that cross the plasma membranes of both cells. [11] With a lumen diameter of about 1.2 to 2.0 nm, [2] [12] the pore of a gap junction channel is wide enough to allow ions and even medium-size molecules like signaling molecules to flow from one cell to the next, [2] [13] thereby connecting the two cells' cytoplasm.
Gap junction proteins. Gap junction α (GJA) proteins. GJA1, Cx43, gap junction alpha-1 protein; GJA2, Cx38, gap junction alpha-2 protein; GJA3, Cx46, gap junction alpha-3 protein; GJA4, Cx37, gap junction alpha-4 protein; GJA5, Cx40, gap junction alpha-5 protein; GJA6, Cx33 gap junction alpha-6 protein; GJA7, Cx44.3-45.6, gap junction alpha-7 ...
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 junction alpha-1 protein (GJA1), also known as connexin 43 (Cx43), is a protein that in humans is encoded by the GJA1 gene on chromosome 6. [5] [6] [7] As a connexin, GJA1 is a component of gap junctions, which allow for gap junction intercellular communication (GJIC) between cells to regulate cell death, proliferation, and differentiation. [8]
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.