Structural component of gap junctions (By similarity). Gap junctions are dodecameric channels that connect the cytoplasm of adjoining cells. They are formed by the docking of two hexameric hemichannels, one from each cell membrane (By similarity). Small molecules and ions diffuse from one cell to a neighboring cell via the central pore (By similarity). {ECO:0000250|UniProtKB:P29033, ECO:0000250|UniProtKB:Q02738}. This is the function of ENSG00000189433 (GJB4, gap junction protein beta 4).