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Two TMS K+ and water channel (conducts K+ (KD = 8 mM); blocked by Na+ (190 mM) (Renart et al., 2006) and tetrabutylammonium (Iwamoto et al., 2006)). Ion permeation occurs by ion-ion contacts in single file fashion through the selectivity filter (Köpfer et al. 2014). A narrow pore lined with four arrays of carbonyl groups is responsible for ion selectivity, whereas a conformational change of the four inner transmembrane helices (TMS2) is involved in gating (Baker et al. 2007). Two gates have been identified; one is located at the inner bundle crossing and is activated by H+ while the second gate is in the selectivity filter (Rauh et al. 2017). The C-terminal domain mediates pH modulation (Hirano et al., 2011Pau et al., 2007). KcsA exhibits a global twisting motion upon gating (Shimizu et al., 2008).  Activity is influenced by the phase of the lipid bilayer (Seeger et al. 2010), and occupancy of nonannular lipid binding sites increases the stability of the tetrameric complex (Triano et al. 2010).  The open conformation of KcsA can disturb the bilayer integrity and catalyze the flipping of phospholipids (Nakao et al. 2014).  This protein is identical to the KcsA orthologue (P0A333) in Streptomyces coelicolor.  The stability of the pre domain in KcsA is stabilized by GCN4 (Yuchi et al. 2008).  The potential role of pore hydration in channel gating has been evaluated (Blasic et al. 2015).  Having multiple K+ ions bound simultaneously is required for selective K+ conduction, and a reduction in the number of bound K+ ions destroys the multi-ion selectivity mechanism utilized by K+ channels (Medovoy et al. 2016).  The channel accomodates K+ and H2O molecules alternately in a K+-H2O-K+-H2O  series through the channel (Kratochvil et al. 2016). Insertion of KcsA is spontaneous and directional as the cytosolic part of the protein does not translocate across the membrane barrier. Charged residues, not hydrophobic residues, are crucial for insertion of the unfolded protein into the membrane via electrostatic interactions between membrane and protein.  A two-step mechanism was proposed. An initial electrostatic attraction between membrane and protein represents the first step prior to insertion of hydrophobic residues into the hydrocarbon core of the membrane (Altrichter et al. 2016). Bend, splay, and twist distinguish KcsA gate opening, filter opening, and filter-gate coupling, respectively (Mitchell and Leibler 2017). Details of the water permeability have been presented. Water flow through KcsA is halved by 200 mM K+ in the aqueous solution, which indicates an effective K+ dissociation constant in that range for a singly occupied channel. (Hoomann et al. 2013). A parameterized MARTINI program can be used to predict the hinging motions of the protein (Li et al. 2019). Activation of KcsA is initiated by proton binding to the pH gate upon an intracellular drop in pH which prompts a conformational switch, leading to a loss of affinity for potassium ions at the selectivity filter and therefore to channel inactivation (Rivera-Torres et al. 2016). An alteration in the conformational equilibrium of the intracellular K+-gate is one of the fundamental mechanisms underlying the dysfunctions of K+ channels caused by disease-related mutations (Iwahashi et al. 2020). Folding and misfolding of KcsA monomers during assembly and tetramerization has been examined (Song et al. 2021). The flexible C-terminus stabilizes KcsA tetramers at a neutral pH with decreased stabilization at acidic pH (Howarth and McDermott 2022). Under equilibrium conditions, in the absence of a transmembrane voltage, both water and K+ occupy the selectivity filter of the KcsA channel in the closed conductive state (Ryan et al. 2023).

Accession Number:P0A334
Protein Name:Voltage-gated potassium channel
Molecular Weight:17694.00
Species:streptomyces lividans [1916]
Number of TMSs:2
Location1 / Topology2 / Orientation3: Cell membrane1 / Multi-pass membrane protein2
Substrate potassium(1+), water

Cross database links:

DIP: DIP-29626N
Pfam: PF07885   

Gene Ontology

GO:0008076 C:voltage-gated potassium channel complex
GO:0005249 F:voltage-gated potassium channel activity
GO:0006813 P:potassium ion transport

References (8)

[1] “A prokaryotic potassium ion channel with two predicted transmembrane segments from Streptomyces lividans.”  Schrempf   7489706
[2] “Proteomics on full-length membrane proteins using mass spectrometry.”  le Coutre   10757971
[3] “Single potassium ion seeks open channel for transmembrane travels: tales from the KcsA structure.”  Gouaux   9782060
[4] “The structure of the potassium channel: molecular basis of K+ conduction and selectivity.”  Doyle   9525859
[5] “Molecular architecture of full-length KcsA: role of cytoplasmic domains in ion permeation and activation gating.”  Cortes   11158168
[6] “Structure of the KcsA channel intracellular gate in the open state.”  Liu   11573095
[7] “Energetic optimization of ion conduction rate by the K+ selectivity filter.”  Morais-Cabral   11689935
[8] “Chemistry of ion coordination and hydration revealed by a K+ channel-Fab complex at 2.0 A resolution.”  Zhou   11689936
1BL8   1F6G   1J95   1JQ1   1JQ2   1JVM   1K4C   1K4D   1R3I   1R3J   [...more]

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