Gazing into the gap

Gap junctions are a ubiquitous feature of multicellular life, allowing cells to pass particular classes of biomolecules directly to their neighbors. It is clear that these channels are not just nonspecific pores, but it has been difficult to determine what establishes their specificity. Skerrett et al., whose work appears on page 349, developed a cell perfusion system that allowed them to identify the residues lining an intact gap junction channel. The work helps answer lingering questions about earlier structural models, and identifies some unusual features of gap junctions.

Previous studies determined the basic structure of a gap junction, in which one membrane-spanning α-helix from each subunit of the channel is exposed to the interior of the pore, but this does not reveal what types of residues line the pore or how...