Pannexins constitute a new family of gap junction type proteins. They are highly conserved in worms, mollusks, insects and mammals and are predicted to have four transmembrane regions, two extracellular loops, one intracellular loop and intracellular N- and C-termini. Besides the connexin proteins, Pannexin 1 and 2 seem to be molecular components of neuronal gap junctions ("electrical synapses") that are thought to form connections between principal cells in the hippocampus. Functional expression in paired Xenopus oocytes indicated that pannexins are capable of forming communicating junctions. In addition to forming gap junction channels in paired oocytes, Pannexin 1 can also form a mechanosensitive and ATP-permeable channel in the nonjunctional plasma membrane. Pannexin 1 and 3 are both glycoproteins with a cell surface distribution profile and life cycle dynamics distinct from connexin 43. Pannexin 3 expression was prevalent in skin and cartilage. In transiently expressing cells both pannexin 1 and 3 were incapable of forming intercellular channels but assembled into functional cell surface channels. Suggested roles in the ischemic death of neurons, schizophrenia, inflammation and tumor suppression have drawn attention for properties and cellular functions of pannexins.
gap junction protein pannexin 3; Pannexin-3; PANX3