The dynamic Nexus: gap junctions control protein localization and mobility in distinct and surprising ways

Area of Science:

• Cell Biology
• Membrane Biology
• Biophysics

Background:

• Gap junction (GJ) channels are crucial for cell-to-cell communication, enabling the transfer of ions, metabolites, and signaling molecules.
• These channels, formed by connexin (Cx) proteins, aggregate into plaques at cell appositions, creating a supramolecular structure called the GJ Nexus.
• While connexin stability in GJ plaques is understood, the dynamics of other GJ Nexus components remain largely unexplored.

Purpose of the Study:

• To investigate the mobility and dynamics of proteins within the GJ Nexus.
• To determine how the movement of GJ Nexus components influences plaque structure and function.
• To characterize the interactions and localization of various proteins within the GJ plaque.

Main Methods:

• Colocalization analysis was employed to assess the distribution of GJ Nexus components and other membrane proteins relative to GJ plaques.
• Fluorescence recovery after photobleaching (FRAP) was used to measure the mobility of tagged Nexus-associated proteins.
• The impact of connexin protein mobility on the dynamics of associated proteins was evaluated.

Main Results:

• Colocalization studies revealed differential exclusion and penetration of various proteins within GJ plaques, with some molecules like Aquaporin 4 and EAAT2b being excluded, while others like Cx30, ZO-1, and Occludin were highly penetrant.
• FRAP experiments demonstrated that the mobility of connexin proteins directly affects the diffusion dynamics of associated cytoplasmic and membrane-embedded proteins within the GJ plaque.
• These findings highlight that the GJ Nexus is not static but a dynamic entity with proteins exhibiting distinct binding and diffusion parameters.

Conclusions:

• The GJ Nexus functions as a dynamic membrane organelle, not merely a static assembly of proteins.
• The mobility of connexin proteins is a key determinant of the overall dynamics and stability of the GJ Nexus.
• Understanding the dynamic nature of the GJ Nexus provides new insights into cellular communication and metabolic exchange.