Channelpedia

Kir5.1

Description: potassium inwardly-rectifying channel, subfamily J, member 16
Gene: Kcnj16     Synonyms: 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


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Gene

RGD ID Chromosome Position Species
61824 10 100514180-100515949 Rat
62115 11 110829347-110889282 Mouse
1343172 17 68071426-68131749 Human

Kcnj16 : potassium inwardly-rectifying channel, subfamily J, member 16


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Transcript

Acc No Sequence Length Source
NM_053314 n/A n/A NCBI
NM_010604 n/A n/A NCBI
NM_018658 n/A n/A NCBI
NM_170741 n/A n/A NCBI
NM_170742 n/A n/A NCBI

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Ontology

Accession Name Definition Evidence
GO:0016021 integral to membrane Penetrating at least one phospholipid bilayer of a membrane. May also refer to the state of being buried in the bilayer with no exposure outside the bilayer. When used to describe a protein, indicates that all or part of the peptide sequence is embedded in the membrane. IEA
GO:0016020 membrane Double layer of lipid molecules that encloses all cells, and, in eukaryotes, many organelles; may be a single or double lipid bilayer; also includes associated proteins. IEA

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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]).


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Protein


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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]).


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Distribution


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Expression

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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Functional


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Kinetics


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Model

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]).


References

1037

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

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).

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).

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).

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).

1022

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).

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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Credits

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