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Molecular basis of calmodulin tethering and Ca2+-dependent inactivation of L-type Ca2+ channels

G S Pitt1, R D Zühlke, A Hudmon

  • 1Department of Molecular and Cellular Physiology, Stanford University Medical School, Stanford, California 94305, USA. gp2004@columbia.edu

The Journal of Biological Chemistry
|June 16, 2001
PubMed

Insights

Calcium-dependent inactivation (CDI) of L-type calcium channels is regulated by calmodulin (CaM) tethering. This study reveals a novel mechanism where CaM binding to two sites slows inactivation, with IQ motif interaction accelerating it.

Area of Science:

  • Molecular and Cellular Biology
  • Ion Channel Physiology
  • Biochemistry

Background:

  • Calcium-dependent inactivation (CDI) of L-type Ca(2+) channels is crucial for regulating Ca(2+) influx in excitable cells.
  • Calmodulin (CaM) is implicated as the Ca(2+) sensor, but its constitutive tethering mechanism remains unclear.

Purpose of the Study:

  • To elucidate the mechanism of Ca(2+) sensor (CaM) tethering to L-type Ca(2+) channels.
  • To investigate the role of CaM tethering sites and Ca(2+) concentrations in CDI regulation.

Main Methods:

  • Site-directed mutagenesis to identify CaM tethering regions on the alpha(1C) subunit C-terminal tail.
  • Biochemical assays using synthetic peptides to characterize CaM-binding properties.
  • Electrophysiological studies to assess the impact on channel inactivation.

Main Results:

  • Ca(2+)-insensitive CaM tethering occurs at the alpha(1C) C-terminal tail, dependent on nanomolar Ca(2+) concentrations.
  • Two specific amino acid stretches within the C-terminal tail support CaM tethering and contain CaM-binding sequences.
  • Peptide studies revealed differential CaM-binding affinities and Ca(2+) dependencies for these sequences.

Conclusions:

  • A novel mechanism for CDI is proposed, where CaM (apoCaM) is constitutively tethered at two sites, actively slowing inactivation.
  • Relief of this braking effect, mediated by CaM C-terminal lobe binding to the IQ motif, accelerates CDI.
  • This provides new insights into the regulation of L-type Ca(2+) channel function.

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