Figure 3.

General connexin/innexin structures forming gap junctions and “hemi-channels”. Vertebrates connexins have three cysteine residues (left) in each of their extracellular loops, while invertebrates innexins have only two cysteines per loop (right). Both connexins and innexins have four transmembrane domains (orange tubes) connected by one cytoplasmic loop (black curve), and have both NH₂ and CO₂H terminals in the cytosol.