IMR Press / FBL / Volume 7 / Issue 4 / DOI: 10.2741/tang

Frontiers in Bioscience-Landmark (FBL) is published by IMR Press from Volume 26 Issue 5 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on as a courtesy and upon agreement with Frontiers in Bioscience.

Calmodulin modulation of proteins involved in excitation-contraction coupling
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1 Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas, USA
Academic Editor:Hector Valdivia
Front. Biosci. (Landmark Ed) 2002, 7(4), 1583–1589;
Published: 1 June 2002
(This article belongs to the Special Issue The structure and function of calcium release channels)

Muscle excitation-contraction coupling is, in large part, regulated by the activity of two proteins. These are the ryanodine receptor (RyR), which is an intracellular Ca2+ release channel and the dihydropyridine receptor (DHPR), which is a voltage gated L-type calcium channel. In skeletal muscle, the physical association between RyR1 and L-type Ca2+ channels is required for muscle excitation-contraction coupling. RyRs also regulate intracellular Ca2+ homeostasis, thereby contributing to a variety of cellular functions in different tissues. A wide variety of modulators directly regulate RyR1 activity and, consequentially, alter both excitation-contraction coupling and calcium homeostasis. Calmodulin, one of these cellular modulators, is a ubiquitously expressed 17 kDa Ca2+ binding protein containing four E-F hands, which binds to RyR1 at both nanomolar and micromolar Ca2+ concentrations. Apocalmodulin (Ca2+ free calmodulin) is a partial agonist, while Ca2+calmodulin is an inhibitor of RyR1. This conversion of calmodulin from an activator to an inhibitor is due to Ca2+ binding to the two C-terminal sites on calmodulin. Calmodulin can also modulate the L-type Ca2+ channel in the transverse tubule membrane, producing either inactivation or facilitation of the channel upon elevation of the local Ca2+ concentrations. Calmodulin binds to a region on RyR1 corresponding to amino acids 3614-3643 and to a region in the carboxy-terminal tail of the L-type Ca2+ channel α1 subunit. However, these calmodulin binding motifs on both proteins bind to undetermined motifs on the other protein, suggesting that they represent more general protein-protein interaction motifs. These findings raise questions about the role of calmodulin in excitation-contraction coupling in skeletal muscle.

Ryanodine receptor (RyR)
Dihydropyridine receptor (DHPR)
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