Structural insights into the gating mechanism of human Cx43/GJA1 gap junction channel

Connexin family proteins assemble into hexameric hemichannels in a cell membrane, which dock together between two adjacent membranes to form gap junction intercellular channels (GJIChs). The most ubiquitously expressed connexin Cx43 plays important roles in numerous biological processes. Here we report cryo-EM structures of Cx43 GJIChs at 3.1–3.6 Å resolutions, which show dynamic conformational changes of N-terminal helices (NTHs) caused by pH change or C-terminal truncation. Cx43 GJIChs in a channel-closing condition contain 12 protomers in gate-covering NTH (GCN) conformation, while those in opening conditions have varying compositions of GCNs and pore-lining NTHs (PLNs) resulting in various pore dimensions and electrostatic surface potentials. GCN-to-PLN transition accompanies π-helix formation in the first transmembrane helix (TM1), movement of TM2-4 that creates a side opening to the membrane, and structural stabilization of the cytoplasmic loop. Our study provides structural insights into the intercellular ion/metabolite transfer and the lateral lipid transport through Cx43 GJICh.