Calcium induced N-terminal gating and pore collapse in connexin-46/50 gap junctions.

Gap junctions facilitate electrical and metabolic coupling essential for tissue function. Under ischemic conditions (., heart attack or stroke), elevated intracellular calcium (Ca) levels uncouple these cell-to-cell communication pathways to protect healthy cells from cytotoxic signals. Using single-particle cryo-EM, we elucidate details of the Ca-induced gating mechanism of native connexin-46/50 (Cx46/50) gap junctions. The resolved structures reveal Ca binding sites within the channel pore that alter the chemical environment of the permeation pathway and induce diverse occluded and gated states through N-terminal domain remodeling. Moreover, subunit rearrangements lead to pore collapse, enabling steric blockade by the N-terminal domains, reminiscent of the "iris model" of gating proposed over four decades ago. These findings unify and expand key elements of previous gating models, providing mechanistic insights into how Ca signaling regulates gap junction uncoupling and broader implications for understanding cell stress responses and tissue protection.