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J Biol Chem. 2006 Aug 4;281(31):21577-81. Epub 2006 Jun 14.

The crystal structure of the primary Ca2+ sensor of the Na+/Ca2+ exchanger reveals a novel Ca2+ binding motif.

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  • 1Department of Physiology and the Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA.


The Na+/Ca2+ exchanger is a plasma membrane protein that regulates intracellular Ca2+ levels in cardiac myocytes. Transport activity is governed by Ca2+, and the primary Ca2+ sensor (CBD1) is located in a large cytoplasmic loop connecting two transmembrane helices. The binding of Ca2+ to the CBD1 sensory domain results in conformational changes that stimulate the exchanger to extrude Ca2+. Here, we present a crystal structure of CBD1 at 2.5A resolution, which reveals a novel Ca2+ binding site consisting of four Ca2+ ions arranged in a tight planar cluster. This intricate coordination pattern for a Ca2+ binding cluster is indicative of a highly sensitive Ca2+ sensor and may represent a general platform for Ca2+ sensing.

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