KCNN4
Domain
Transmembrane helices S5 and S6 form the ion channel pore, which is surrounded bymembrane embedded helices S1 to S4 (PubMed:29724949). The S4-S5 linker, which contains two distinct helices, undergoes conformational changes upon calmodulin binding to open the channel pore (PubMed:29724949).
Function
Intermediate conductance calcium-activated potassium channel that mediates the voltage-independent transmembrane transfer of potassium across the cell membrane through a constitutive interaction with calmodulin which binds the intracellular calcium allowing its opening (PubMed:10026195, PubMed:10961988, PubMed:11425865, PubMed:15831468, PubMed:17157250, PubMed:18796614, PubMed:26148990, PubMed:9326665, PubMed:9380751, PubMed:9407042). The current is characterized by a voltage-independent activation, an intracellular calcium concentration increase-dependent activation and a single-channel conductance of about 25 picosiemens (PubMed:9326665, PubMed:9380751, PubMed:9407042). Also presents an inwardly rectifying current, thus reducing its already small outward conductance of potassium ions, which is particularly the case when the membrane potential displays positive values, above + 20 mV (PubMed:9326665, PubMed:9380751, PubMed:9407042). Controls calcium influx during vascular contractility by being responsible of membrane hyperpolarization induced by vasoactive factors in proliferative vascular smooth muscle cell types (By similarity). Following calcium influx, the consecutive activation of KCNN4 channel leads to a hyperpolarization of the cell membrane potential and hence an increase of the electrical driving force for further calcium influx promoting sustained calcium entry in response to stimulation with chemotactic peptides (PubMed:26418693). Required for maximal calcium influx and proliferation during the reactivation of naive T-cells (PubMed:17157250, PubMed:18796614). Plays a role in the late stages of EGF-induced macropinocytosis through activation by PI(3)P (PubMed:24591580).
Involvement in disease
Dehydrated hereditary stomatocytosis 2
DHS2
An autosomal dominant hemolytic anemia characterized by primary erythrocyte dehydration. Erythrocytes exhibit decreased total cation and potassium content that are not accompanied by a proportional net gain of sodium and water. Affected individuals typically manifest mild to moderate compensated hemolytic anemia, with an increased erythrocyte mean corpuscular hemoglobin concentration and a decreased osmotic fragility, both of which reflect cellular dehydration. Their red cells exhibit a panel of various shape abnormalities such as elliptocytes, hemighosts, schizocytes, and very rare stomatocytic cells. Complications such as splenomegaly and cholelithiasis, resulting from increased red cell trapping in the spleen and elevated bilirubin levels, respectively, may occur.
None
The disease is caused by variants affecting the gene represented in this entry.
Post-translational modifications
Phosphorylation at His-358 by NDKB activates the intermediate conductance calcium-activated potassium channel activity, and conversely it's dephosphorylation by PHPT1 inhibits this activity.
Sequence Similarities
Belongs to the potassium channel KCNN family. KCa3.1/KCNN4 subfamily.
Tissue Specificity
Widely expressed in non-excitable tissues.
Cellular localization
- Cell membrane
- Multi-pass membrane protein
- Cell projection
- Ruffle membrane
- Targeted to membrane ruffles after EGF stimulation.
Alternative names
IK1, IKCA1, KCA4, SK4, KCNN4, Intermediate conductance calcium-activated potassium channel protein 4, SKCa 4, SKCa4, hSK4, Gardos channel, IKCa1, KCa3.1, Putative Gardos channel, hKCa4, hIK1