Altered formation of hemichannels and gap junction channels caused by C-terminal connexin-32 mutations

Area of Science:

• Cell biology
• Molecular neuroscience
• Biophysics

Background:

• Connexins (Cxs) assemble into hexameric hemichannels.
• Hemichannels dock to form gap junction channels, crucial for intercellular communication.
• X-linked Charcot-Marie-Tooth disease is associated with mutations in Cx32.

Purpose of the Study:

• To investigate the functional consequences of C-terminal Cx32 mutations on hemichannel and gap junction channel formation.
• To determine if hemichannels are direct precursors to gap junction channels.
• To identify structural requirements for Cx32 hemichannel assembly and function.

Main Methods:

• Utilized the Xenopus oocyte expression system.
• Assessed hemichannel formation and function at the plasma membrane via depolarization.
• Quantified gap junction channel assembly by measuring hemichannel incorporation after cell-cell contact.

Main Results:

• Wild-type Cx32 hemichannels, when undocked, can function as open channels activated by depolarization.
• Demonstrated that hemichannels are direct precursors to gap junction channels.
• Five of eleven Cx32 mutants failed to form cell surface hemichannels.
• Four mutants formed hemichannel precursors but had reduced gap junction assembly efficiency.
• Two mutants exhibited normal channel formation.
• A minimum Cx32 length, including Arg-215, is necessary for cell surface hemichannel expression.
• Progressive shortening of the C-terminal domain reduced hemichannel incorporation into complete channels.

Conclusions:

• Hemichannels serve as direct precursors for functional gap junction channels.
• C-terminal Cx32 mutations associated with Charcot-Marie-Tooth disease disrupt hemichannel formation or subsequent gap junction assembly.
• The Cx32 C-terminal domain length is critical for both hemichannel surface expression and efficient gap junction formation.