Calcium release-activated calcium channel protein 1 is a calcium selective

ion channel Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of ...

that in humans is encoded by the ''ORAI1''

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 b ...

. Orai channels play an important role in the activation of

T-lymphocytes A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell rec ...

. The loss of function mutation of Orai1 causes

severe combined immunodeficiency Severe combined immunodeficiency (SCID), also known as Swiss-type agammaglobulinemia, is a rare genetic disorder characterized by the disturbed development of functional T cells and B cells caused by numerous genetic mutations that result in dif ...

(SCID) in humans The mammalian orai family has two additional homologs, Orai2 and Orai3. Orai proteins share no homology with any other ion channel family of any other known proteins. They have 4

transmembrane A transmembrane protein (TP) is a type of integral membrane protein that spans the entirety of the cell membrane. Many transmembrane proteins function as gateways to permit the transport of specific substances across the membrane. They frequentl ...

domains and form hexamers.

Structure and function

Orai channels are activated upon the depletion of internal calcium stores, which is called the "store-operated" or the "capacitative" mechanism. They are molecular constituents of the "calcium release activated calcium currents" ( ICRAC). Upon activation of

phospholipase C Phospholipase C (PLC) is a class of membrane-associated enzymes that cleave phospholipids just before the phosphate group (see figure). It is most commonly taken to be synonymous with the human forms of this enzyme, which play an important role i ...

by various cell surface receptors,

inositol trisphosphate Inositol trisphosphate or inositol 1,4,5-trisphosphate abbreviated InsP3 or Ins3P or IP3 is an inositol phosphate signaling molecule. It is made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid that is located in the p ...

is formed that releases calcium from the

endoplasmic reticulum The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...

. The decreased calcium concentration in the endoplasmic reticulum is sensed by the STIM1 protein. STIM1 clusters upon the depletion of the calcium stores and forms " puncta", and relocates near the plasma membrane, where it activates Orai1 via protein-protein interaction. In 2012, a 3.35-

angstrom The angstromEntry "angstrom" in the Oxford online dictionary. Retrieved on 2019-03-02 from https://en.oxforddictionaries.com/definition/angstrom.Entry "angstrom" in the Merriam-Webster online dictionary. Retrieved on 2019-03-02 from https://www.m ...

(Å)

crystal structure In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns t ...

of the

Drosophila ''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many s ...

Orai channel, which shares 73% sequence identity with human Orai1 within its

transmembrane region Cell surface receptors (membrane receptors, transmembrane receptors) are receptors that are embedded in the plasma membrane of cells. They act in cell signaling by receiving (binding to) extracellular molecules. They are specialized integral ...

, was published. The structure, thought to show the closed state of the channel, revealed that a single channel is composed of six Orai subunits, with the

transmembrane domain A transmembrane domain (TMD) is a membrane-spanning protein domain. TMDs generally adopt an alpha helix topological conformation, although some TMDs such as those in porins can adopt a different conformation. Because the interior of the lipid b ...

s arranged in concentric rings around a central aqueous pore formed exclusively by the first transmembrane helix of each subunit. Transmembrane helices 2 and 3 surround TM1 and are hypothesized to shield it from the surrounding

lipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many ...

and provide structural support. The fourth transmembrane helix forms the outermost layer.

Ligands

;Inhibitors *

CM-4620 CM-4620 is a drug which acts as a selective inhibitor of the calcium channel A calcium channel is an ion channel which shows selective permeability to calcium ions. It is sometimes synonymous with voltage-gated calcium channel, although there a ...

References

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