Lumen cues calcium release

Calcium release from lumenal stores is sensitive to the redox state of the ER lumen, as shown by Takayasu Higo, Katsuhiko Mikoshiba (University of Tokyo, Japan), and colleagues. The group has identified the first ER lumenal protein that controls IP₃-regulated calcium channels (IP₃Rs).The opening of IP₃Rs is tightly controlled by cytosolic conditions. Most scientists assume that conditions in the ER also regulate channel opening, but the evidence was minimal. To find any relevant regulators in the ER, the authors used a lumenal domain of IP₃R1 to fish out binding proteins. They discovered ERp44, whose association with IP₃R1 blocked IP₃-induced calcium release.

But the binding of ERp44 and IP₃R1, and subsequent channel blockage, depended on...