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Paramecium calmodulin mutants defective in ion channel regulation can bind calcium and undergo calcium-induced

O R Jaren1, S Harmon, A F Chen

  • 1Department of Biochemistry, University of Iowa College of Medicine, Iowa City, Iowa 52242-1109, USA.

Biochemistry
|June 8, 2000
PubMed

Insights

Calmodulin (CaM) mutants alter calcium binding and conformational switching. These changes disrupt the allosteric mechanism, leading to faulty ion channel regulation, impacting signal transduction pathways.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cell Signaling

Background:

  • Calmodulin (CaM) is a crucial eukaryotic protein regulating signal transduction via calcium ion binding.
  • Vertebrate CaM's domain interactions modulate calcium affinities, enabling sequential cleft opening.
  • Domain-specific mutants of Parameciumcalmodulin (PCaM) offer insights into homologous domain functions in ion channel regulation.

Purpose of the Study:

  • To dissect the roles of the two homologous half-molecule domains in Parameciumcalmodulin (PCaM).
  • To investigate how domain-specific mutations in PCaM affect calcium binding affinities and conformational changes.
  • To understand the impact of altered allosteric mechanisms on ion channel regulation.

Main Methods:

  • Utilized domain-specific mutants of Parameciumcalmodulin (PCaM).
  • Monitored calcium binding via changes in intrinsic fluorescence of tyrosine 138 (Y138) in site IV.
  • Analyzed conformational changes through secondary structure and Stokes radius measurements.

Main Results:

  • Calcium binding induced similar directional changes in secondary structure and Stokes radius for mutants and wild-type PCaM, but with varying magnitudes.
  • PCaM sites III and IV exhibited higher calcium affinities than rat CaM sites and PCaM mutants altered between sites I and II.
  • All mutants underwent conformational switching in the same direction as wild-type PCaM upon calcium saturation, but to a lesser extent.

Conclusions:

  • Altered properties of switching among partially saturated PCaM species, rather than end-state conformation or target interaction deficits, explain disrupted allosteric mechanisms.
  • Faulty ion channel regulation in PCaM mutants stems from disruptions in the dynamic switching among intermediate calcium-bound states.
  • Understanding these domain-specific allosteric effects is critical for deciphering CaM's role in eukaryotic signal transduction.

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