Calexcitin B is a new member of the sarcoplasmic calcium-binding protein family.
Calexcitin (CE) is a calcium sensor protein that has been implicated in associative learning. The CE gene was previously cloned from the long-finned squid, Loligo pealei, and the gene product was shown to bind GTP and modulate K(+) channels and ryanodine receptors in a Ca(2+)-dependent manner. We cloned a new gene from L. pealei, which encodes a CE-like protein, here named calexcitin B (CE(B)). CE(B) has 95% amino acid identity to the original form. Our sequence analyses indicate that CEs are homologous to the sarcoplasmic calcium-binding protein subfamily of the EF-hand superfamily. Far and near UV circular dichroism and nuclear magnetic resonance studies demonstrate that CE(B) binds Ca(2+) and undergoes a conformational change. CE(B) is phosphorylated by protein kinase C, but not by casein kinase II. CE(B) does not bind GTP. Western blot experiments using polyclonal antibodies generated against CE(B) showed that CE(B) is expressed in the L. pealei optic lobe. Taken together, the neuronal protein CE represents the first example of a Ca(2+) sensor in the sarcoplasmic calcium-binding protein family.
Gombos
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Division of Molecular and Structural Biology, Ontario Cancer Institute and Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 2M9, Canada.
Jeromin
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Mal
T K
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Chakrabartty
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Ikura
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D000595:Amino Acid Sequence; D001483:Base Sequence; D029742:Caenorhabditis elegans Proteins; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002942:Circular Dichroism; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet
D029742:Caenorhabditis elegans Proteins; D002135:Calcium-Binding Proteins; D019204:GTP-Binding Proteins; C102751:cex-2 protein, C elegans