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Title: Endogenously bound calmodulin is essential for the function of the inositol 1,4,5-trisphosphate receptor
Authors: Nadif Kasri, Nael ×
Török, Katalin
Galione, Antony
Garnham, Clive
Callewaert, Geert
Missiaen, Ludwig
Parys, Jan
De Smedt, Humbert #
Issue Date: Mar-2006
Publisher: American Society for Biochemistry and Molecular Biology
Series Title: Journal of Biological Chemistry vol:281 issue:13 pages:8332-8338
Abstract: Calmodulin (CaM) is a ubiquitous Ca2+ sensor protein that plays an important role in regulating a large number of Ca2+ channels, including the inositol 1,4,5-trisphosphate receptor (IP3R). Despite many efforts, the exact mechanism by which CaM regulates the IP3R still remains elusive. Here we show, using unidirectional 45Ca2+ flux experiments on permeabilized L15 fibroblasts and COS-1 cells, that endogenously bound CaM is essential for the proper activation of the IP3R. Removing endogenously bound CaM by titration with a high affinity (pM) CaM-binding peptide derived from smooth muscle myosin light-chain kinase (MLCK peptide) strongly inhibited IP3-induced Ca2+ release. This inhibition was concentration- and time-dependent. Removing endogenously bound CaM affected the maximum release capacity but not its sensitivity to IP3. A mutant peptide with a strongly reduced affinity for CaM did not affect inhibited IP3-induced Ca2+ release. Furthermore, the inhibition by the MLCK peptide was fully reversible. Re-adding exogenous CaM, but not CaM1234, reactivated the IP3R. These data suggest that, by using a specific CaM-binding peptide, we removed endogenously bound CaM from a high affinity CaM-binding site on the IP3R, and this resulted in a complete loss of the IP3R activity. Our data support a new model whereby CaM is constitutively associated with the IP3R and functions as an essential subunit for proper functioning of the IP3R.
URI: 
ISSN: 0021-9258
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Physiology Section (-)
Laboratory of Molecular and Cellular Signaling
× corresponding author
# (joint) last author

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