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0  structures 90  species 0  interactions 342  sequences 12  architectures

Family: SK_channel (PF03530)

Summary: Calcium-activated SK potassium channel

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Calcium-activated SK potassium channel Provide feedback

No Pfam abstract.

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR015449

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].

SK channels are thought to play an important role in the functioning of all excitable tissues. To date, 3 subtypes (designated SK1-SK3) have been cloned, each of which possesses a different tissue expression profile: SK1 channels are expressed in the heart; SK2 channels are found in the adrenal gland; and SK3 channels are known to be present in skeletal muscle [PUBMED:8781233]. SK channels have a single-channel conductance of 2-20 pS and are activated by rises in cytosolic calcium with half maximal activation in the 400-800 nM range [PUBMED:2432249, PUBMED:7993625]. Unlike BK channels, they are voltage insensitive and unaffected by low concentrations of TEA, charybdotoxin, or iberiotoxin. However, they are potently blocked by the bee venom apamin [PUBMED:6099412, PUBMED:2430185], tubocurarine, and quaternary salts of bicuculline [PUBMED:9280156, PUBMED:10390643]. A new series of compounds that block SK channels include dequalinium

Gene Ontology

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Domain organisation

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Alignments

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Representative proteomes NCBI
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RP35
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RP55
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RP75
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Format an alignment

  Seed
(10)
Full
(342)
Representative proteomes NCBI
(301)
Meta
(0)
RP15
(35)
RP35
(51)
RP55
(113)
RP75
(179)
Alignment:
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We make all of our alignments available in Stockholm format. You can download them here as raw, plain text files or as gzip-compressed files.

  Seed
(10)
Full
(342)
Representative proteomes NCBI
(301)
Meta
(0)
RP15
(35)
RP35
(51)
RP55
(113)
RP75
(179)
Raw Stockholm Download   Download   Download   Download   Download   Download   Download    
Gzipped Download   Download   Download   Download   Download   Download   Download    

You can also download a FASTA format file containing the full-length sequences for all sequences in the full alignment.

External links

MyHits provides a collection of tools to handle multiple sequence alignments. For example, one can refine a seed alignment (sequence addition or removal, re-alignment or manual edition) and then search databases for remote homologs using HMMER3.

Pfam alignments:

HMM logo

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Trees

This page displays the phylogenetic tree for this family's seed alignment. We use FastTree to calculate neighbour join trees with a local bootstrap based on 100 resamples (shown next to the tree nodes). FastTree calculates approximately-maximum-likelihood phylogenetic trees from our seed alignment.

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Curation and family details

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Curation View help on the curation process

Seed source: PRINTS
Previous IDs: none
Type: Family
Author: Griffiths-Jones SR
Number in seed: 10
Number in full: 342
Average length of the domain: 110.00 aa
Average identity of full alignment: 53 %
Average coverage of the sequence by the domain: 20.18 %

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 22.9 22.9
Trusted cut-off 23.4 23.4
Noise cut-off 21.8 20.5
Model length: 119
Family (HMM) version: 9
Download: download the raw HMM for this family

Species distribution

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