Architecture of a CRAC
The calcium release–activated calcium (CRAC) channel generates intracellular calcium signals in response to depletion of calcium from the endoplasmic reticulum. Hou et al. report a high-resolution crystal structure of Orai, the CRAC channel pore from Drosophila melanogaster . Six Orai subunits surround a central pore that extends into the cytosol. The pore is in a closed conformation that is stabilized by anions binding to a basic region near the intracellular side. A ring of glutamates on the extracellular side form a selectivity filter. The channel architecture allows calcium permeation while regulating the flow to prevent overloading the cell with calcium. X. Hou, L. Pedi, M. M. Diver, S. B. Long, Crystal structure of the calcium release–activated calcium channel Orai. Science 338 , 1308–1313 (2012). [Abstract][Full Text]