A CNG channel consists of four subunits around a central pore. Each protein subunit consists 6 transmembrane segments (S1-S6), a P-loop, intracellular amino terminal region, and carboxy terminal region. The P-loop and S6 segments around the pore, which plays a role in<unk>  conduction. There is a<unk><unk>  binding domain (CNBD) and connection region to the S6 segment in the carboxy terminal. There is a post-CNDB region in the amino terminal. Alpha subunits<unk><unk><unk>  channel alpha-subunits include<unk><unk><unk>  channel alpha 1<unk><unk><unk>  channel alpha 2<unk><unk><unk>  channel alpha 3<unk><unk><unk>  channel alpha 4 Beta subunits<unk><unk><unk>  channel beta-subunits include:<unk><unk><unk>  channel beta 1<unk><unk><unk>  channel beta 3 Pore The structure of the pore is similar to other<unk>  channels that contain P-loops. The P-loop enters the membrane of the pore from the extracellular side and exits to the intracellular side. The P loop enters as an alpha helix and exists as an uncoiled strand. Helices that cover the inner membrane line the channel. These also form a 6 helix bundle that signifies the entrance. In order to open the pore, a conformational change must occur in the inner 6 helix bundle.<unk><unk>  binding domain A<unk><unk> -binding domain is an intracellular domain located in the C-terminus region and has a similar sequence to other<unk><unk> -binding proteins. The domain is believed to be made up of a β-pleated sheet and two α-helices. The β-pleated sheet is made up of eight antiparallel strands. The α helices are named the B and C helices. A ligand initially binds to the β-pleated sheet, and through allosteric regulation causes the movement to an α-helix toward the β-pleated sheet. The α-helix is flexible in closed channels. When an α-helix of a CNGA1 subunit is in close proximity to another α-helix, they form intersubunit disulfide bonds. This occurs mainly in closed channels, inhibiting movement of the α-helix towards the β-pleated sheet. When a ligand binds to the β-pleated sheet, this bound<unk><unk>  stabilizes the movement of the α-helix toward the β-pleated sheet in each subunit, pulling the α-helices away from each other. Illustration of a<unk>  with a cAMP binding domain. C-linker The C-linker is a region that connects the CNBD to the S6 segment. The C-linker region contributes to the contact between channel subunits as well as promotes tetramerization, the forming of tetramers. There are many residues that play a role in modulation of CNG channels. This process uses metals such as nickel, zinc, copper, and magnesium. The C-linker region is involved in the coupling of ligand binding to the opening of the pore. The C linker region forms disulfide bonds with N-terminal regions. Disulfide bonds alter the channel function therefore they most likely lie close to the tertiary structure. Disulfide bonds decrease the free energy of the open state compared to the closed state. The specific cysteine residue C481 on the C-linker region is located only a few amino acids away from the binding domain. In the closed state C481 is nonreactive; C481 must undergo a conformational change so that it is accessible for the opening of the channel. Disulfide bonds form between neighboring subunits and C481. Simultaneously there is a C35 cysteine residue at the N-terminal of the C-linker region that can reach two C481 residues, making a favorable disulfide bond compared to a C481-C481 bond. S6 region Spontaneous disulfide bond formation is state-dependent, implying that the conformational change in the helix bundle is affiliated with channel gating. When the CNG<unk>  channels are closed, the cytoplasmic ends of the S6 helices are in close proximity to each other. Small cations are able to move through an opening, which implies that the<unk> is beyond the helix bundle and that S6 helices are in conjunction with conformational changes in the selectivity filter. P region The P region forms a loop, the pore loop, connecting the S5 and S6 regions, which extend to the central axis of the channel.<unk> ic properties are determined by the residues in the loop between S5 and S6 transmembrane segments. The P region dictates the<unk>  selectivity of the<unk><unk><unk> <unk>  channel, which also determine the pore diameter of CNG channels. The P region functions as a channel<unk> since it prevents<unk>  permeation in the closed state. The pore may be hindered by small conformational changes in this region. The P region acts as an<unk>  selectivity filter that changes structure in the open conformation. In the open state, four identical subunits contribute a single P-loop region, which forms a selectivity filter.
Cyclic nucleotide–gated ion channel
Voltage-gated ion channel
G protein-gated ion channel
Mechanosensitive channels
Neurotransmitter transporter
Glutamate transporter
Norepinephrine transporter
Tropomyosin receptor kinase A