Voltage-gated potassium channels (VGKCs) are transmembrane channels specific for potassium and sensitive to voltage changes in the cell's membrane potential. It mainly contains alpha and beta subunits. Based on sequence homology of the hydrophobic transmembrane cores, the alpha subunits are grouped into 12 classes, whcih are labeled Kvα1-12 (Kv1.1, Kv1.2, Kv1.3, Kv1.3, Kv1.4, Kv1.5, Kv1.6, Kv1.7, Kv1.8, Kv2.1, Kv2.2, Kv3.1, Kv3.2, Kv4.1, Kv4.2, Kv4.3, Kv5.1, Kv6.1, Kv6.2, Kv6.3, Kv6.4, Kv7.1, Kv7.2, Kv7.3, Kv7.4, Kv7.5, Kv8.1, Kv8.2, Kv9.1, Kv9.2, Kv9.3, Kv10.1, Kv10.2, Kv11.1, Kv11.2, Kv11.3, Kv12.1, Kv12.2, Kv12.3). Beta subunits are auxiliary proteins that associate with alpha subunits and they do not conduct current on their own but rather modulate the activity of Kv channels. They are grouped into 12 classes (Kvβ1, Kvβ2, Kvβ3, minK, MiRP1, MiRP2, MiRP3, KCNE1-like, KCNIP1, KCNIP2, KCNIP3, KCNIP4) ^[1].

Typically, vertebrate voltage-gated K⁺ channels are tetramers of four identical subunits arranged as a ring, each contributing to the wall of the trans-membrane K⁺ pore. Each subunit is composed of six membrane spanning hydrophobic α-helical sequences, as well as a voltage sensor in S4. The intracellular side of the membrane contains both amino and carboxy termini ^[2].

Procyanidin B1 directly binds to Kv10.1 channel and inhibits its currents, without increasing intracellular Ca2+. Further, three amino acids (white sphere in the 3D structure viewer), I550, T552, and Q557 in the C-linker domain of Kv10.1 were found critical for forming the binding pocket of Procyanidin B1 with Kv10.1 channel ^[4].

Kv7.2: The residues of W236A, L299A, I300A, S303A and F305A (red sphere in the 3D structure viewer) form the binding pocket with Ebio1 ^[5]. The docking and electrophysiology methods were used to identify critical residues involved in ML252 sensitivity. Most notably, Kv7.2[W236F] or Kv7.3[W265F] mutations strongly attenuate ML252 sensitivity. This tryptophan residue in the pore is also required for sensitivity to certain activators, including retigabine and ML213 ^[15].

Kv1.3: Substitutions at Leu(346) and Leu(353) in S(5), and Ala(413), Val(417), Ala(421), Pro(423), and Val(424) in S(6), (red sphere in the 3D structure viewer) cause the most dramatic effect on correolide binding to K(v)1.3 ^[15].

Site-directed mutagenesis to define the binding site (HERG F805C and HERG R823W), was not restored by channel blockers ^[16]. Toxin mutagenesis study was identified the residues that are important for the binding of BeKm-1 to the human ERG K⁺ (HERG) channel. The most critical residues (Tyr-11, Lys-18, Arg-20, Lys-23) are located in the α-helix and following loop whereas the "traditional" functional site of other short scorpion toxins is formed by residues from the β-sheet ^[17]. Ala-scanning mutagenesis of the pore domain of Kv1.5 identified the amino acids Thr479, Thr480, Val505, Ile508, Val512, and Val516 as important residues for block by AVE0118 ^[21].

These residues of F557, L622, T623, S624, L650, M651, Y652, I655, F656 (Kv11.1, blue sphere in the 3D structure viewer) form the binding pocket with Phenanthrene ^[3]. A single S5 residue (Thr556 red sphere in the 3D structure viewer in hERG) may been shown to activate hERG with RPR260243. RPR260243 has no significant effects on the human cardiac Na+ channel or the KCNQ1/KCNE1 cardiac K⁺ channel, which are also linked with LQTS, thus showing high selectivity for hERG. Moreover, RPR260243 inhibits the erg3 channel ^[6]. Besides, PD-118057 ^[7], PD-307243^[8], NS1643 (black sphere in the 3D structure viewer: S620, S631)^[9], NS3623 (black sphere in the 3D structure viewer: S620, S631) ^[10], A-935142^[11], ICA-105574^[12], KB130015 (white sphere in the 3D structure viewer: Y652)^[13], and mallotoxin^[14] has also been shown to activate hERG. Non-selective KCNQ2-5/3 activators have shown efficacy in pre-clinical and clinical studies. However, more selective pharmacological profiles, including greater KCNQ sub-type-selective activation, could provide efficacy with fewer side effects ^[23]. One such compound, ICA-27243, sub-type selectively enhances the activation of KCNQ2/3 channels and also exhibits efficacy in pre-clinical anticonvulsant models ^[23]. The binding site of non-selective KCNQ2-5/3 openers maps to the S5-S6 pore domain and is altered by mutation of a tryptophan residue (Trp236 in KCNQ2, Trp265 in KCNQ3) conserved among KCNQ2-5 channels ^[23]. Here we report that the activity of the KCNQ2/3 selective opener ICA-27243 is not affected by these Trp mutations and does not map to the S5-S6 domain. Rather, the selective activity of ICA-27243 is determined by a novel site within the S1-S4 voltage-sensor domain (VSD) of KCNQ channels. The sub-type-selective activity of ICA-27243 may arise from greater sequence diversity of KCNQ family members within the ICA-27243 binding pocket, allowing for more selective small molecule-protein interactions. (R)-L3 effects on current amplitude could be unaffected (I235A, M238A, L239A, and V241A), significantly increased (R237A and H240A) or decreased (L236A) by the respective amino acid exchange. These results indicate, that L236, R237, and H240 are involved in the modulatory mechanism of (R)-L3 ^[20].

(VU0405601 and ML-T531) and a newly synthesized compound (LUF7244) were found to be negative allosteric modulators of dofetilide binding to the Kv11.1 channel ^[18]. A single-point mutation of the predicted key histidine into cysteine in the rat Kv7.2 subunit, rKv7.2(H558C), resulted in a loss of effects of DHEAS on muscarinic Kv7 current suppression ^[19]. Binding of the N-terminal domain or a positively charged lipophilic compound such as quinidine interacts with the hydrophobic moieties on S6 in the bound state. This binding can orientate S6 into a conformation which resembles the normal C-type inactivated state. This is the probable mechanism by which drug or N-terminal binding increases the rate of C-type inactivation via an allosteric mechanism ^[22]. In the binding site of Kv3.1, AUT5 and AUT1 make contacts with the side chains from V312 and F315 in the S4 helix, and M362, Y365, I369 and A371 in the S5 helix, which are highly conserved in Kv3.1, Kv3.2 and Kv3.4 ^[22].