Pivoting between calmodulin lobes triggered by calcium in the Kv7.2/calmodulin complex

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.