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Biphasic Ca2+-dependent switching in a calmodulin-IQ domain complex.

D J Black1, Jared Leonard, Anthony Persechini

  • 1Division of Molecular Biology and Biochemistry, University of Missouri, Kansas City, Missouri 64110-2499, USA.

Biochemistry
|June 1, 2006
PubMed
Summary

Calmodulin (CaM) and neuromodulin IQ domain binding exhibits a biphasic Ca2+ switch. Ca2+ binding to CaM

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In calmodulin-IQ domain complexes, the Ca(2+)-free and Ca(2+)-bound forms of the calmodulin C-lobe direct the N-lobe to different binding sites.

Biochemistry·2011

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Calcium Signaling

Background:

  • Calmodulin (CaM) is a crucial calcium-binding protein.
  • Neuromodulin IQ domain interacts with CaM.
  • Understanding CaM-IQ domain dynamics is vital for cellular signaling.

Purpose of the Study:

  • To elucidate the relationship between free Ca2+ concentration and the dissociation constant (Kd) of the CaM-IQ domain complex.
  • To investigate the biphasic nature of Ca2+ binding to CaM and its effect on CaM-IQ complex stability.

Main Methods:

  • Characterization of the CaM-IQ domain complex.
  • Measurement of apparent dissociation constants (Kd) at varying free Ca2+ concentrations.
  • Analysis of Ca2+ binding to CaM's EF hand pairs.

Main Results:

  • The CaM-IQ complex exhibits a biphasic response to free Ca2+ concentration.
  • Ca2+ binding to the C-terminal EF hands increases Kd, while binding to N-terminal EF hands decreases Kd.
  • A bell-shaped Kd-Ca2+ concentration relationship was observed, with a narrow Ca2+ range for CaM release.

Conclusions:

  • CaM-IQ domain complexes act as biphasic Ca2+ switches.
  • Sequential Ca2+ binding to CaM's EF hand pairs drives opposing effects on complex stability.
  • This mechanism allows for CaM release within a specific, narrow free Ca2+ concentration range.

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