Abstract:
Innexins, a large protein family comprising invertebrate gap junction channels, play an essential role in nervous system development and electrical synapse formation. Here we report the cryo-electron microscopy structures of Caenorhabditis elegans innexin-6 (INX-6) gap junction channels at atomic resolution. We find that the arrangements of the transmembrane helices and extracellular loops of the INX-6 monomeric structure are highly similar to those of connexin-26 (Cx26), despite the lack of significant sequence similarity. The INX-6 gap junction channel comprises hexadecameric subunits but reveals the N-terminal pore funnel, consistent with Cx26. The helix-rich cytoplasmic loop and C-terminus are intercalated one-by-one through an octameric hemichannel, forming a dome-like entrance that interacts with N-terminal loops in the pore. These observations suggest that the INX-6 cytoplasmic domains are cooperatively associated with the N-terminal funnel conformation, and an essential linkage of the N-terminal with channel activity is presumably preserved across gap junction families.