Kv8.2

Kv8.2 (also known as RCD3B; KV11.1; MGC120515), encoded by the gene KCNV1, is member 2 of subfamily V. Kv8.2 is identified as a 'silent subunit', and it does not form homomultimers, but forms heteromultimers with several other subfamily members. Through obligatory heteromerization, it exerts a function-altering effect on other potassium channel subunits. This protein is strongly expressed in pancreas and has a weaker expression in several other tissues. [730] NCBI

Visual Representation of Kv8.2 Structure
Methodology for visual representation of structure available here

Analysis of Mutations Located in the Pore Domain Kv8.2

The following figure shows the location of the disease-causing mutations in hKv8.2 in CDSRE patients examined in this study. Three of these, W450G, G459D, and G461R, are located in the pore region of the hKv8.2 α-subunit. The missense mutations G459D and G461R affect the first and second glycine, respectively, of the Gly-Tyr-Gly motif, the characteristic potassium channel signature sequence. To understand the functional consequences of these mutations, the corresponding mutations (W467G, G476D, and G478R) were introduced into mKv8.2, and their effect on subunit localization in COS7L cells was examined. Like mKv8.2, the expression of either mKv8.2-W467G-EGFP, mKv8.2-G476D-EGFP, or mKv8.2-G478R-EGFP resulted in an intracellular localization [1753]

Voltage-gated K+ channels selectively transfer potassium ions through the plasma membrane in response to depolarization. The ion-conducting core of voltage-gated K+ channels is composed of four Kv-alpha subunits, which also possess the voltage sensor. According to structural similarities, members of the Kv family were initially divided into four subfamilies (Kv1–Kv4), the mammalian equivalents of the Drosophila Shaker, Shab, Shaw, and Shal gene products, respectively. These Kv subunits give rise to functional homotetrameric K+ channels, when they are expressed heterologously in Xenopus laevis oocytes (for review see [496]). Coexpression of members of the same subfamily may result in functional heterotetrameric channels and currents with properties different from those of the homotetramers of the parent subunits. The current of these heteromeric Kv channels was also identified in native tissues [733], [734]. Subunits belonging to different Kv1–Kv4 subfamilies do not coassemble [731]. The selectivity within the subfamilies is ensured by the specific N-terminal tetramerization domains [598], [599].

Mutated (B6-Kv8.2) Kinetics whit Kv2.1 in CHO cells

Coexpression of mKv2.1 with B6-Kv8.2 produced significantly greater suppression than SJL-Kv8.2 for voltage steps between 0 mV and +60 mV. Further, B6-Kv8.2, but not SJL-Kv8.2, had a significant effect on the kinetics of activation that was limited to a single test potential (0 mV) without a corresponding change in voltage dependence. Neither Kv8.2 isoform differed in the magnitude of cumulative inactivation evoked by moderate-frequency pulse trains, but SJL-Kv8.2 did evoke a greater time-dependent decay in whole-cell current [730]

hKv8.2 and hKv2.1 Co transfected in CHO Cell Kinetics

Coexpression of Kv2.1 with either R7K or M285R Kv8.2 variants resulted in significantly greater suppression of Kv2.1-mediated current compared with wild-type Kv8.2 for voltage steps from 0 mV to +60 mV [730]

Kv8.2 Expressed in the Brain

Members of the Kv2 family are expressed in the nervous system and underlie the neuronal delayed rectifier K+ current, which is important for limiting membrane excitability, particularly under conditions of repetitive stimulation [91]. In the hippocampus, which is a region of particular importance for seizure generation, Kv2.1 is the major contributor to the delayed rectifier potassium current [732] and colocalizes with Kv8.2 in hippocampal pyramidal neurons (Allen Institute for Brain Science (2009) Allen mouse brain atlas. Available at: http:// mouse.brain-map.org. Accessed August 13, 2010.)

Whole-brain expression of Kcnv2 does not differ between strains B6 and SJL. We further investigated strain-dependent expression in the hippocampus for three reasons: first, previous EEG studies showed that seizures in Scn2aQ54 likely originate in the hippocampus; second, Kcnv2 transcripts are enriched in the hippocampus; and, third, the biophysical differences described above were counterintuitive and suggested more complex physiology. RNA was isolated from dissected hippocampi of 8-wk-old B6 and SJL mice for quantitative RT-PCR (qRT-PCR) analysis [730]

Membrane Translocation

Kv8.2 can form functional heterotetramers with Kv2 subunits and influence membrane translocation and channel properties [648], [731].

Kcnv2 transgene-mediated transfer of seizure susceptibility is observed in mice, as well as human variants that alter delayed rectifier K+ currents. These results identify KCNV2 as an epilepsy gene in mice and humans. [730]

Cone Dystrophy

Mutations in KCNV2 have been proposed as the molecular basis for cone dystrophy with supernormal rod electroretinogram. KCNV2 codes for the modulatory voltage-gated potassium channel α-subunit, Kv8.2, which is incapable of forming functional channels on its own. Functional heteromeric channels are however formed with Kv2.1 in heterologous expression systems, with both α-subunit genes expressed in rod and cone photoreceptors [1753]

Epilepsy

Kv8.2 also contributes to Epilepsy [730]

Kv2.1

Kv8.2 changes the kinetics of Kv2.1 (see kinetics for more info) [730]

Contributors: Rajnish Ranjan, Michael Schartner