Calmodulin Binding to Connexin 35: Specializations to Function as an Electrical Synapse

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Gap junctions mediate intercellular communication, with calmodulin binding regulating calcium-dependent uncoupling.
• Electrical synapses in neuronal networks require stable function despite calcium fluctuations.
• Connexin 35 (Cx35) is a key protein in electrical synapses, homologous to mammalian Connexin 36 (Cx36).

Purpose of the Study:

• To investigate the properties and functional consequences of calmodulin binding to Cx35.
• To understand how Cx35 maintains stable electrical synapse function under varying calcium conditions.

Main Methods:

• Studied Cx35 calmodulin binding sites and their response to calcium.
• Utilized mutations to assess the role of specific calmodulin binding sites.
• Investigated the impact of calcium/calmodulin-dependent protein kinase II (CaMKII) activity.

Main Results:

• Cx35 exhibits specialized calmodulin binding sites that confer relative resistance to moderate calcium increases.
• A C-terminal calmodulin binding site mediates uncoupling at low micromolar calcium, a process prevented by mutations.
• A second, low-affinity calmodulin binding site exists in the cytoplasmic loop.
• Milder calcium stimuli enhance coupling via CaMKII without calmodulin interference.

Conclusions:

• Cx35's calmodulin binding sites are adapted to prevent frequent uncoupling in neuronal electrical synapses.
• Cx35 maintains stable electrical coupling except under extreme intracellular calcium conditions.
• These adaptations are crucial for reliable neuronal network function.