Calcium release activated channel

Calcium release-activated channels (CRAC) are specialized plasma membrane Ca ion channels. When calcium ions (Ca) are depleted from the endoplasmic reticulum (a major store of Ca) of mammalian cells, the CRAC channel is activated to slowly replenish the level of calcium in the endoplasmic reticulum. The Ca Release-activated Ca (CRAC) Channel (CRAC-C) Family (TC# 1.A.52) is a member of the Cation Diffusion Facilitator (CDF) Superfamily. These proteins typically have between 4 and 6 transmembrane α-helical spanners (TMSs). The 4 TMS CRAC channels arose by loss of 2TMSs from 6TMS CDF carriers, an example of 'reverse' evolution'.