Structure of the ductin channel

Gap junctions appear to be essential components of metazoan animals providi ng a means of direct means of communication between neighboring cells. They are sieve-like structures which allow cell-cell movement of cytosolic solu tes below 1000 MW. The major role of gap junctions would appear to be homeo static giving rise to groups of cells which act as functional units. Ductin is the major core component of gap junctions and recent structural data sh ows it to be a four alpha-helical bundle which fits particularly well into a low resolution model of the gap junction channel. Ductin is also the main membrane component of the vacuolar H+-ATPase that is found in all eukaryot es and it seems likely that the gap junction channel first evolved as a hou sing for the rotating spindle of these proton pumps. Because ductin protrud es little from the membrane, other proteins are required to bring cell surf aces close enough together to form gap junctions. Such proteins may include connexins, a large family of proteins found in vertebrates.