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Biochim Biophys Acta. 2006 Nov;1763(11):1161-8. Epub 2006 Sep 20.

Calcium signals mediated by STIM and Orai proteins--a new paradigm in inter-organelle communication.

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Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 108 North Greene Street, Baltimore, MD 21201, USA.


In all cells Ca2+ signals are key to controlling a spectrum of cellular responses. Ca2+ signals activated by phospholipase C-coupled receptors have two components-rapid Ca2+ release from ER stores followed by slower Ca2+ entry from outside the cell. The coupling process between ER and PM to mediate this "store-operated" Ca2+ entry process has remained a molecular and mechanistic mystery. Through a combination of high throughput screening and molecular physiological approaches, the machinery and mechanism of this process have been elucidated. Two proteins are key to the coupling process. STIM1, a single spanning membrane protein with an unpaired Ca2+ binding EF-hand functions as the sensor of ER luminal Ca2+ and through redistribution in the ER transduces information directly to the PM. Orai1, a tetra-spanning PM protein, functions as the highly Ca2+ selective channel in the PM that is gated through interactions with the store-activated ER Ca2+ sensor. This molecular pas-de-deux between ER and PM components represents not only a crucial signaling pathway, but also a new paradigm in inter-organelle communication.

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