Asynchronous subunit transitions prime acetylcholine receptor activation

Communication at synapses is facilitated by postsynaptic receptors, which convert a chemical signal into an electrical response. For ligand-gated ion channels, agonist binding triggers rapid transitions through intermediate states leading to a transient open-pore conformation, with these transitions shaping the post-synaptic response. Here, we determine structures of the muscle-type nicotinic acetylcholine receptor in unliganded, mono-liganded, and di-liganded states. Agonist binding to a single site stabilizes a closed structure where an entire principal agonist-binding subunit transitions to an active-like conformation, while the other unoccupied principal subunit remains inactive, albeit poised for activation. Uniting this intermediate structure with single-channel recordings informs a sequential activation mechanism where asynchronous subunit transitions prime the receptor for activation, a finding with implications for an entire superfamily of pentameric ligand-gated ion channels.