The gating mechanism in cyclic nucleotide-gated ion channels

Abstract

Cyclic nucleotide-gated (CNG) channels mediate transduction in several sensory neurons. These channels use the free energy of CNs’ binding to open the pore, a process referred to as gating. CNG channels belong to the superfamily of voltage-gated channels, where the motion of the α-helix S6 controls gating in most of its members. To date, only the open, cGMP-bound, structure of a CNG channel has been determined at atomic resolution, which is inadequate to determine the molecular events underlying gating. By using electrophysiology, site-directed mutagenesis, chemical modification, and Single Molecule Force Spectroscopy, we demonstrate that opening of CNGA1 channels is initiated by the formation of salt bridges between residues in the C-linker and S5 helix. These events trigger conformational changes of the α-helix S5, transmitted to the P-helix and leading to channel opening. Therefore, the superfamily of voltage-gated channels shares a similar molecular architecture but has evolved divergent gating mechanisms.

An iris diaphragm mechanism to gate a cyclic nucleotide-gated ion channel

“…5c ). Although more recently the role of S6 in CNG channel gating has been challenged 35 , similar mechanisms involving a twist of the C-linkers to pull apart the S6 helices and eventually gate the channel have been suggested in earlier studies 12 , 36 . Given that the C-terminal end of the bundle-crossing helix S6 is attached to the C-linker at a radial distance of ~1 nm from the axis, we propose a simple mechanical model where the C-linker acts as a mechanical lever.…”

Voltage vs. Ligand I: Structural basis of the intrinsic flexibility of S3 segment and its significance in ion channel activation

“…We hypothesized that segmental rigidity is associated with largescale motions of specific domains during inactivation as well as systemic flexibility and small-scale molecular motions are preferentially involved during activation in specific regions of the V-sensor. In favor of this, some reports indicate that, in flexible channels (BK Ca , SK, CNG) gating is not mainly mediated by the large bending of the distal part of S6 (such as in K V , Na V , or Ca V channels) but small conformational rearrangements in the selectivity filter and the S4-S5/S5-P-helix connecting loops, which play a major role on this process [30,117,118]. Obtaining this type of evidence will help to corroborate or rule out our conjectures.…”

“…These motions are associated with specific regions of the VSD, including the S3 segment, as well as linkers S3-S4L and S4-S5L [9,[27][28][29]. In CNG channels, which are virtually voltage-independent, the opening of the pore has evolved in strict dependence on the cyclic nucleotide-binding through conformational changes involving the S4-S5L [30].…”

A cyclic nucleotide‐gated channel in the brain regulates olfactory modulation through neuropeptide F in fruit fly Drosophila melanogaster

“…CNG channels form heterodimers as three A subunits and one B subunit. In mammals, four genes encode A subunits (CNGA1, CNGA2, CNGA3, and CNGA4) and two genes encode B subunits (CNGB1 and CNGB3; Kaupp & Seifert, ; Mazzolini et al, ). In insects, CNG channels have been studied in fruit fly Drosophila melanogaster (Baumann, Frings, Godde, Seifert, & Kaupp, ; Miyazu, Tanimura, & Sokabe, ), honeybee Apis mellifera (Gisselmann et al, ), and moths Heliothis virescens and Manduca sexta (Krannich & Stengl, ; Krieger, Strobel, Vogl, Hanke, & Breer, ).…”