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Updated: May 3, 2026
Pull-down of Calmodulin-binding Proteins
Published on: January 23, 2012
Pivoting between calmodulin lobes triggered by calcium in the Kv7.2/calmodulin complex
Alessandro Alaimo1, Araitz Alberdi1, Carolina Gomis-Perez1
1Unidad de Biofísica, CSIC, UPV/EHU, Universidad del País Vasco, Leioa, Spain.
Abstract:
Kv7.2 (KCNQ2) is the principal molecular component of the slow voltage gated M-channel, which strongly influences neuronal excitability. Calmodulin (CaM) binds to two intracellular C-terminal segments of Kv7.2 channels, helices A and B, and it is required for exit from the endoplasmic reticulum. However, the molecular mechanisms by which CaM controls channel trafficking are currently unknown. Here we used two complementary approaches to explore the molecular events underlying the association between CaM and Kv7.2 and their regulation by Ca(2+). First, we performed a fluorometric assay using dansylated calmodulin (D-CaM) to characterize the interaction of its individual lobes to the Kv7.2 CaM binding site (Q2AB). Second, we explored the association of Q2AB with CaM by NMR spectroscopy, using (15)N-labeled CaM as a reporter. The combined data highlight the interdependency of the N- and C-lobes of CaM in the interaction with Q2AB, suggesting that when CaM binds Ca(2+) the binding interface pivots between the N-lobe whose interactions are dominated by helix B and the C-lobe where the predominant interaction is with helix A. In addition, Ca(2+) makes CaM binding to Q2AB more difficult and, reciprocally, the channel weakens the association of CaM with Ca(2+).
Insights
Calmodulin (CaM) binding to Kv7.2 channels is crucial for neuronal excitability and channel trafficking. Calcium ions alter CaM
Area of Science:
- Neuroscience
- Molecular Biology
- Biophysics
Background:
- Kv7.2 (KCNQ2) channels are key regulators of neuronal excitability.
- Calmodulin (CaM) binding to Kv7.2 C-terminal helices A and B is essential for endoplasmic reticulum exit.
- The precise molecular mechanisms of CaM-mediated Kv7.2 channel trafficking remain unclear.
Purpose of the Study:
- To elucidate the molecular mechanisms of CaM interaction with Kv7.2 channels.
- To investigate the role of Ca(2+) in regulating the CaM-Kv7.2 association.
- To characterize the CaM binding site on Kv7.2 (Q2AB).
Main Methods:
- Fluorometric assays using dansylated calmodulin (D-CaM) to study CaM lobe interactions with Q2AB.
- NMR spectroscopy with (15)N-labeled CaM to analyze Q2AB-CaM association.
- Investigating the Ca(2+) dependence of these interactions.
Main Results:
- CaM's N- and C-lobes show interdependent binding to Q2AB.
- Ca(2+) binding induces a pivot in the binding interface, favoring helix B interaction with the N-lobe and helix A with the C-lobe.
- Ca(2+) hinders CaM binding to Q2AB, and Kv7.2 weakens CaM's Ca(2+) association.
Conclusions:
- Ca(2+) dynamically regulates the CaM-Kv7.2 interaction interface.
- This Ca(2+)-dependent regulation impacts channel trafficking and neuronal function.
- Understanding this interplay is vital for comprehending Kv7.2 channel regulation.
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