Secretagogin is a hexa EF-hand protein, which has been identified as a novel potential tumour marker. In the present study, we show that secretagogin binds four Ca2+ ions (log K1=7.1±0.4, log K2=4.7±0.6, log K3=3.6±0.7 and log K4=4.6±0.6 in physiological salt buffers) with a [Ca2+]0.5 of approx. 25 μM. The tertiary structure of secretagogin changes significantly upon Ca2+ binding, but not upon Mg2+ binding, and the amount of exposed hydrophobic surface in secretagogin increases upon Ca2+ binding, but not upon Mg2+ binding. These properties suggest that secretagogin belongs to the ‘sensor’ family of Ca2+-binding proteins. However, in contrast with the prototypical Ca2+ sensor calmodulin, which interacts with a very large number of proteins, secretagogin is significantly less promiscuous. Only one secretagogin-interacting protein was reproducibly identified from insulinoma cell lysates and from bovine and mouse brain homogenates. This protein was identified as SNAP-25 (25 kDa synaptosome-associated protein), a protein involved in Ca2+-induced exocytosis in neurons and in neuroendocrine cells. Kd was determined to be 1.2×10−7 M in the presence of Ca2+ and 1.5×10−6 M in the absence of Ca2+. The comparatively low Ca2+ affinity for secretagogin and the fact that it undergoes Ca2+-induced conformational changes and interacts with SNAP-25 raise the possibility that secretagogin may link Ca2+ signalling to exocytotic processes.
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Research Article|
December 11 2006
Binding of calcium ions and SNAP-25 to the hexa EF-hand protein secretagogin Available to Purchase
Annika Rogstam;
Annika Rogstam
*Department of Biophysical Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
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Sara Linse;
Sara Linse
*Department of Biophysical Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
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Anders Lindqvist;
Anders Lindqvist
§Department of Molecular and Cellular Physiology, Lund University, SE-221 00 Lund, Sweden
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Peter James;
Peter James
‡Department of Protein Technology, Lund University, SE-221 84 Lund, Sweden
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Ludwig Wagner;
Ludwig Wagner
†Department of Internal Medicine III, Forschungslabor 7H, University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria
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Tord Berggård
Tord Berggård
1
*Department of Biophysical Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden
‡Department of Protein Technology, Lund University, SE-221 84 Lund, Sweden
1To whom correspondence should be addressed (email [email protected]).
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Publisher: Portland Press Ltd
Received:
June 19 2006
Revision Received:
August 22 2006
Accepted:
August 30 2006
Accepted Manuscript online:
August 30 2006
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London
2007
Biochem J (2007) 401 (1): 353–363.
Article history
Received:
June 19 2006
Revision Received:
August 22 2006
Accepted:
August 30 2006
Accepted Manuscript online:
August 30 2006
Citation
Annika Rogstam, Sara Linse, Anders Lindqvist, Peter James, Ludwig Wagner, Tord Berggård; Binding of calcium ions and SNAP-25 to the hexa EF-hand protein secretagogin. Biochem J 1 January 2007; 401 (1): 353–363. doi: https://doi.org/10.1042/BJ20060918
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