KCNE3

1000857442ENSG00000175538ENSMUSG00000035165Q9Y6H6Q9WTW2NM_005472NM_001360466NM_001360467NP_005463NP_001347395NP_001347396Potassium voltage-gated channel, Isk-related family, member 3 (KCNE3), also known as MinK-related peptide 2 (MiRP2) is a protein that in humans is encoded by the KCNE3 gene. Potassium voltage-gated channel, Isk-related family, member 3 (KCNE3), also known as MinK-related peptide 2 (MiRP2) is a protein that in humans is encoded by the KCNE3 gene. Voltage-gated potassium channels (Kv) represent the most complex class of voltage-gated ion channels from both functional and structural standpoints. Their diverse functions include regulating neurotransmitter release, heart rate, insulin secretion, neuronal excitability, epithelial electrolyte transport, smooth muscle contraction, and cell volume. KCNE3 encodes a member of the five-strong KCNE family of voltage-gated potassium (Kv) channel ancillary or β subunits. KCNE3 is best known for modulating the KCNQ1 Kv α subunit, but it also regulates hERG, Kv2.1, Kv3.x, Kv4.x and Kv12.2 in heterologous co-expression experiments and/or in vivo. Co-assembly with KCNE3 converts KCNQ1 from a voltage-dependent delayed rectifier K+ channel to a constitutively open K+ channel with an almost linear current/voltage (I/V) relationship. KCNQ1-KCNE3 channels have been detected in the basolateral membrane of mouse small intestinal crypts, where they provide a driving force to regulate Cl- secretion. Specific amino acids within the transmembrane segment (V72) and extracellular domain (D54 and D55) of KCNE3 are important for its control of KCNQ1 voltage dependence. D54 and D55 interact electrostatically with R237 in the S4 segment of the KCNQ1 voltage sensor, helping to stabilize S4 in the activated state, which in turn locks open the channel unless the cell is held at a strongly hyperpolarizing (negative) membrane potential. The ability of KCNQ1-KCNE3 channels to remain open at weakly negative membrane potentials permits their activity in non-excitable, polarized epithelial cells such as those in the intestine. KCNE3 also interacts with hERG, and when co-expressed in Xenopus laevis oocytes KCNE3 inhibits hERG activity by an unknown mechanism. It is not known whether hERG-KCNE3 complexes occur in vivo. KCNE3 interacts with Kv2.1 in vitro and forms complexes with it in rat heart and brain. KCNE3 slows Kv2.1 activation and deactivation. KCNE3 can also regulate channels of the Kv3 subfamily, which are best known for permitting ultrarapid firing of neurons because of the extremely fast gating (activation and deactivation). KCNE3 moderately slows Kv3.1 and Kv3.2 activation and deactivation, and moderately speeds their C-type inactivation. It is possible that KCNE3 (and KCNE1 and 2) regulation of Kv3.1 and Kv3.2 helps to increase functional diversity within the Kv3 subfamily. KCNE3 also regulates Kv3.4, augments its current by increasing the unitary conductance and by left-shifting the voltage dependence such that the channel can open at more negative voltages. This may allow Kv3.4-KCNE3 channels to contribute to setting resting membrane potential. KCNE3 inhibits the fast inactivating Kv channel Kv4.3, which generates the transient outward Kv current (Ito) in human cardiac myocytes). similarly, KCNE3 was recently found to inhibit Kv4.2, and it is thought that this regulation modulates spike frequency and other electrical properties of auditory neurons. Kv12.2 channels were found to be inhibited by endogenous KCNE3 (and KCNE1) subunits in Xenopus laevis oocytes. Thus, silencing of endogenous KCNE3 or KCNE1 using siRNA increases the macroscopic current of exogenously expressed Kv12.2. Kv12.2 forms a tripartite complex with KCNE1 and KCNE3 in oocytes, and may do so in mouse brain. Previously, endogenous oocyte KCNE3 and KCNE1 were also found to inhibit exogenous hERG activity and slow the gating of exogenous Kv2.1. KCNE proteins are type I membrane proteins, and each assembles with one or more types of Kv channel α subunit to modulate their gating kinetics and other functional parameters. KCNE3 has a larger predicted extracellular domain, and smaller predicted intracellular domain, in terms of primary structure, when compared to other KCNE proteins. As with other KCNE proteins, the transmembrane segment of KCNE3 is thought to be α-helical, and the extracellular domain also adopts a partly helical structure. KCNE3, like KCNE1 and possibly other KCNE proteins, are thought to make contact with the S4 of one α subunit and the S6 of another α subunit within the tetramer of Kv α subunits in a complex. No studies have as yet reported the number of KCNE3 subunits within a functional channel complex; it is likely to be either 2 or 4.