Structural and Functional Consequences of Connexin 36 (Cx36) Interaction with Calmodulin

Area of Science:

• Neuroscience
• Molecular Biology
• Biophysics

Background:

• Neuronal gap junctions, formed by connexins, facilitate direct electrical communication between neurons.
• Functional plasticity of these junctions is essential for neural circuit function and learning.
• Connexin36 (Cx36) is a key connexin subtype involved in electrical synapses.

Purpose of the Study:

• To investigate the interaction between Cx36 and its binding partners, calmodulin (CaM) and calcium/calmodulin-dependent kinase II (CaMKII).
• To elucidate the role of calcium in regulating these interactions and their functional consequences.
• To determine the structural basis of CaM binding to Cx36.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to determine the solution structure of CaM-Cx36 complex.
• Biochemical assays to assess calcium-dependent binding and channel activity.
• Site-directed mutagenesis to identify key residues involved in binding.

Main Results:

• CaM and CaMKII binding to Cx36 are calcium-dependent.
• Cx36 engages with CaM outside of the gap junction plaque.
• Ca²⁺-loaded CaM directly activates Cx36 channels, a novel mechanism compared to other connexins.
• NMR structure reveals CaM binds Cx36 via hydrophobic interactions involving specific residues (W277, V284).

Conclusions:

• Cx36 acts as a hub for Ca²⁺-loaded CaM binding.
• This interaction is a critical step preceding CaMKII-mediated plasticity at electrical synapses.
• The findings provide new insights into the regulation of electrical synapse function and plasticity.