Protein component of gap junctions which are specialized regions of the plasma membrane formed by a cluster of channels allowing small molecules to diffuse from the cytosol of one cell to that of an adjacent cell. A current model of the gap junction consists of a cluster of gap-junction channels. Both membranes contain connexon hemichannels, composed of a hexamer of an integral membrane protein which is often referred to as connexin. The junction of two adjacent connexons forms a gap-junction channel.
