Structural dynamics in the gating ring of cyclic nucleotide-gated ion channels

For ligand-gated ion channels, the binding of a ligand to an intracellular or extracellular domain generates changes in transmembrane pore- forming helices, which alters ion flow. The molecular mechanism for this allostery, however, remains unknown. Here we explore the structure and conformational rearrangements of the C- terminal gating ring of the cyclic nucleotide - gated channel CNGA1 during activation by cyclic nucleotides with patch- clamp fluorometry. By monitoring fluorescent resonance energy transfer ( FRET) between membrane- resident quenchers and fluorophores attached to the channel, we detected no movement orthogonal to the membrane during channel activation. By monitoring FRET between fluorophores within the C- terminal region, we determined that the C- terminal end of the C- linker and the end of the C- helix move apart when channels open. We conclude that during channel activation, a portion of the gating ring moves parallel to the plasma membrane, hinging toward the central axis of the channel.