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1  structure 48  species 0  interactions 225  sequences 6  architectures

Family: CaKB (PF03185)

Summary: Calcium-activated potassium channel, beta subunit

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This is the Wikipedia entry entitled "Calcium-activated potassium channel beta subunit". More...

Calcium-activated potassium channel beta subunit Edit Wikipedia article

CaKB
PDB 1jo6 EBI.jpg
solution structure of the cytoplasmic n-terminus of the bk beta-subunit kcnmb2
Identifiers
Symbol CaKB
Pfam PF03185
InterPro IPR003930
SCOP 1jo6
SUPERFAMILY 1jo6
TCDB 8.A.14

In molecular biology, the calcium-activated potassium channel beta subunit is a family of proteins comprising the beta subunits of calcium-activated potassium channels.

The functional diversity of potassium channels can arise through homo- or hetero-associations of alpha subunits or association with auxiliary cytoplasmic beta subunits. The beta subunit (which is thought to possess 2 transmembrane domains) increases the calcium sensitivity of the BK channel.[1] It does this by enhancing the time spent by the channel in burst-like open states. However, it has little effect on the durations of closed intervals between bursts, or on the numbers of open and closed states entered during gating.[2]

References[edit]

  1. ^ McManus OB, Helms LM, Pallanck L, Ganetzky B, Swanson R, Leonard RJ (March 1995). "Functional role of the beta subunit of high conductance calcium-activated potassium channels". Neuron 14 (3): 645–50. doi:10.1016/0896-6273(95)90321-6. PMID 7695911. 
  2. ^ Nimigean CM, Magleby KL (March 1999). "The beta subunit increases the Ca2+ sensitivity of large conductance Ca2+-activated potassium channels by retaining the gating in the bursting states". J. Gen. Physiol. 113 (3): 425–40. PMC 2222905. PMID 10051518. 

This article incorporates text from the public domain Pfam and InterPro IPR003930

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Literature references

  1. Wallner M, Meera P, Toro L; , Proc Natl Acad Sci U S A 1999;96:4137-4142.: Molecular basis of fast inactivation in voltage and Ca2+-activated K+ channels: a transmembrane beta-subunit homolog. PUBMED:10097176 EPMC:10097176


External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR003930

Potassium channels are the most diverse group of the ion channel family [PUBMED:1772658, PUBMED:1879548]. They are important in shaping the action potential, and in neuronal excitability and plasticity [PUBMED:2451788]. The potassium channel family is composed of several functionally distinct isoforms, which can be broadly separated into 2 groups [PUBMED:2555158]: the practically non-inactivating 'delayed' group and the rapidly inactivating 'transient' group.

These are all highly similar proteins, with only small amino acid changes causing the diversity of the voltage-dependent gating mechanism, channel conductance and toxin binding properties. Each type of K+ channel is activated by different signals and conditions depending on their type of regulation: some open in response to depolarisation of the plasma membrane; others in response to hyperpolarisation or an increase in intracellular calcium concentration; some can be regulated by binding of a transmitter, together with intracellular kinases; while others are regulated by GTP-binding proteins or other second messengers [PUBMED:2448635]. In eukaryotic cells, K+ channels are involved in neural signalling and generation of the cardiac rhythm, act as effectors in signal transduction pathways involving G protein-coupled receptors (GPCRs) and may have a role in target cell lysis by cytotoxic T-lymphocytes [PUBMED:1373731]. In prokaryotic cells, they play a role in the maintenance of ionic homeostasis [PUBMED:11178249].

All K+ channels discovered so far possess a core of alpha subunits, each comprising either one or two copies of a highly conserved pore loop domain (P-domain). The P-domain contains the sequence (T/SxxTxGxG), which has been termed the K+ selectivity sequence. In families that contain one P-domain, four subunits assemble to form a selective pathway for K+ across the membrane. However, it remains unclear how the 2 P-domain subunits assemble to form a selective pore. The functional diversity of these families can arise through homo- or hetero-associations of alpha subunits or association with auxiliary cytoplasmic beta subunits. K+ channel subunits containing one pore domain can be assigned into one of two superfamilies: those that possess six transmembrane (TM) domains and those that possess only two TM domains. The six TM domain superfamily can be further subdivided into conserved gene families: the voltage-gated (Kv) channels; the KCNQ channels (originally known as KvLQT channels); the EAG-like K+ channels; and three types of calcium (Ca)-activated K+ channels (BK, IK and SK) [PUBMED:11178249]. The 2TM domain family comprises inward-rectifying K+ channels. In addition, there are K+ channel alpha-subunits that possess two P-domains. These are usually highly regulated K+ selective leak channels.

Ca2+-activated K+ channels are a diverse group of channels that are activated by an increase in intracellular Ca2+ concentration. They are found in the majority of nerve cells, where they modulate cell excitability and action potential. Three types of Ca2+-activated K+ channel have been characterised, termed small-conductance (SK), intermediate conductance (IK) and large conductance (BK) respectively [PUBMED:9687354].

BK channels (also referred to as maxi-K channels) are widely expressed in the body, being found in glandular tissue, smooth and skeletal muscle, as well as in neural tissues. They have been demonstrated to regulate arteriolar and airway diameter, and also neurotransmitter release. Each channel complex is thought to be composed of 2 types of subunit: the pore- forming (alpha) subunits and smaller accessory (beta) subunits.

The beta subunit (which is thought to possess 2 TM domains) increases the Ca2+ sensitivity of the BK channel [PUBMED:7695911]. It does this by enhancing the time spent by the channel in burst-like open states. However, it has little effect on the durations of closed intervals between bursts, or on the numbers of open and closed states entered during gating [PUBMED:10051518].

Gene Ontology

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Domain organisation

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  Seed
(10)
Full
(225)
Representative proteomes NCBI
(207)
Meta
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RP15
(26)
RP35
(31)
RP55
(56)
RP75
(119)
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  Seed
(10)
Full
(225)
Representative proteomes NCBI
(207)
Meta
(0)
RP15
(26)
RP35
(31)
RP55
(56)
RP75
(119)
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External links

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Seed source: Pfam-B_2176 (release 6.5)
Previous IDs: none
Type: Family
Author: Mifsud W
Number in seed: 10
Number in full: 225
Average length of the domain: 174.90 aa
Average identity of full alignment: 38 %
Average coverage of the sequence by the domain: 79.42 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 25.0 25.0
Trusted cut-off 25.1 26.3
Noise cut-off 23.7 24.4
Model length: 201
Family (HMM) version: 10
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Species distribution

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Structures

For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the CaKB domain has been found. There are 1 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.

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