Channelpedia

Kir5.1

Description: potassium inwardly-rectifying channel, subfamily J, member 16
Gene: Kcnj16
Alias: Kir5.1, kcnj16, BIR9

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Introduction

Of the 80 different K+ channel genes found in the human genome, 15 belong to the family of inwardly-rectifying potassium (Kir) channels which are further subdivided into seven different classes (Kir1.1–Kir7.1) (Bichet[1041]). The Kir5.1 subunit does not form functional channels by itself and has no related homologs in the mammalian genome (Pessia [1042], Constas [1019]). However, Kir5.1 co-assembles with Kir4.1 to form novel heteromeric Kir4.1/Kir5.1 channels. (Shang [1040])

KCNJ16 (also known as BIR9; KIR5.1; MGC33717) encodes Kir5.1, an integral membrane protein, inward-rectifier type potassium channel, subfamily J, member 16. The encoded protein, which has a greater tendency to allow potassium to flow into a cell rather than out of a cell, can form heterodimers with two other inward-rectifier type potassium channels. It may be involved in the regulation of fluid and pH balance. Three transcript variants encoding the same protein have been found for this gene.

http://www.ncbi.nlm.nih.gov/gene/3773


Experimental data

Rat Kir5.1 gene in CHO host cells
25 °C
show 44 cells
35 °C
show 18 cells

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Gene

Species NCBI gene ID Chromosome Position
Human 3773 17 60383
Mouse 16517 11 59935
Rat 29719 10 31347

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Transcript

Species NCBI accession Length (nt)
Human NM_018658.4 4067
Mouse NM_001252207.1 3718
Rat NM_053314.3 1770

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Protein Isoforms

Species Uniprot ID Length (aa)
Human Q9NPI9 418
Mouse Q9Z307 419
Rat P52191 419

Isoforms

Transcript
Length (nt)
Protein
Length (aa)
Variant
Isoform

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Post-Translational Modifications

PTM
Position
Type

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Structure

Given the tetrameric nature of the K+ channel pore it is assumed that the central ion conduction pathway is not formed unless all four of the gating helices are in their ‘open’ conformation. Therefore, one structural model to explain the existence of K+ channel subconductance states is that these sublevels originate at the helix-bundle crossing due to successive movements of the four gating helices from the closed to open states, each movement producing a ‘partial’ opening of the channel on the way to the fully open state (Bezanilla [1044]). An alternative model proposed by Chapman & VanDongen suggests that the sublevels seen in the voltage-gated Kv2.1 channel originate from asymmetric conformations adopted by the selectivity filter in response to individual movements of the four gating helices (Chapman 2005 [1046]). Either way, both models assume that the allosteric interactions between identical subunits in a homomeric channel are highly cooperative, resulting in rapid transitions between the sublevels which are not resolved in the timescales of most single-channel recordings, making their analysis difficult, especially when obscured by noise and filtering. This behaviour, therefore, gives the appearance of a smooth and binary transition between the open and closed states (Bezanilla [1044], Chapman 2005 [1046]).

Kir5.1 predicted AlphaFold size

Species Area (Å2) Reference
Human 4710.34 source
Mouse 4513.12 source
Rat 4481.34 source

Methodology for AlphaFold size prediction and disclaimer are available here


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Biophysics

The simplest models of ion channel gating are binary and alternate between two discrete permeation states: open and closed. The movement between these two states is thought to be controlled by a ‘gate’ which physically impedes the flow of ions in the closed state but which moves out of the way during the open state. However, such simple models of channel gating are challenged by the observation of intermediate conductance, or ‘subconductance’ levels, such as those seen in heteromeric Kir4.0/Kir5.1 channels as well as many other types of ion channel (Bezanilla [1044], Fox [1045], Chapman 2005 [1046], Chapman 1997 [1047]).


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Expression and Distribution

basolateral small conductance K+ channel in the distal nephron as well as pH-sensitive K+ channels in chemosensitive neurons (Pessia 1996 [1042], Pessia 2001 [1020]). Likewise, heteromeric Kir4.2/Kir5.1 channels have been reported in hepatic and pancreatic tissues (Pessia 2001 [1020], Pearson [205], Hill [1031]).


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Interaction

The functional properties of heteromeric Kir4.1/Kir5.1 channels are profoundly different to their parental subunits; homomeric Kir4.1 channels are only mildly sensitive to intracellular pH (IC50 ∼ 6.0) and have a single channel conductance of approximately 10 pS. By contrast, heteromeric Kir4.1/Kir5.1 channels are highly sensitive to intracellular pH (IC50 ∼ 6.8) and have a single channel conductance of ∼45 pS with multiple short-lived, subconductance states (Pessia 1996 [1042], Pessia 2001 [1020], Konstas [1019], Rapedius [1043], Tanemoto [1013], Giwa [1024], Xu [1023]).


References

205

Pearson WL et al. Expression of a functional Kir4 family inward rectifier K+ channel from a gene cloned from mouse liver.
J. Physiol. (Lond.), 1999 Feb 1 , 514 ( Pt 3) (639-53).

Tanemoto M et al. In vivo formation of a proton-sensitive K+ channel by heteromeric subunit assembly of Kir5.1 with Kir4.1.
J. Physiol. (Lond.), 2000 Jun 15 , 525 Pt 3 (587-92).

Konstas AA et al. Identification of domains that control the heteromeric assembly of Kir5.1/Kir4.0 potassium channels.
Am. J. Physiol., Cell Physiol., 2003 Apr , 284 (C910-7).

Xu H et al. Modulation of kir4.1 and kir5.1 by hypercapnia and intracellular acidosis.
J. Physiol. (Lond.), 2000 May 1 , 524 Pt 3 (725-35).

Hill CE et al. Cloning, expression, and localization of a rat hepatocyte inwardly rectifying potassium channel.
Am. J. Physiol. Gastrointest. Liver Physiol., 2002 Feb , 282 (G233-40).

Shang L et al. Kir5.1 underlies long-lived subconductance levels in heteromeric Kir4.1/Kir5.1 channels from Xenopus tropicalis.
Biochem. Biophys. Res. Commun., 2009 Oct 23 , 388 (501-5).

Bichet D et al. Merging functional studies with structures of inward-rectifier K(+) channels.
Nat. Rev. Neurosci., 2003 Dec , 4 (957-67).

Bezanilla F The origin of subconductance levels in voltage-gated K+ channels.
J. Gen. Physiol., 2005 Aug , 126 (83-6).

Fox JA Ion channel subconductance states.
J. Membr. Biol., 1987 , 97 (1-8).

Chapman ML et al. K channel subconductance levels result from heteromeric pore conformations.
J. Gen. Physiol., 2005 Aug , 126 (87-103).


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