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1  structure 65  species 0  interactions 90  sequences 4  architectures

Family: Connexin43 (PF03508)

Summary: Gap junction alpha-1 protein (Cx43)

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This is the Wikipedia entry entitled "Gap junction protein, alpha 1". More...

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Gap junction alpha-1 protein (Cx43) Provide feedback

No Pfam abstract.

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR013124

The connexins are a family of integral membrane proteins that oligomerise to form intercellular channels that are clustered at gap junctions. These channels are specialised sites of cell-cell contact that allow the passage of ions, intracellular metabolites and messenger molecules (with molecular weight less than 1-2kDa) from the cytoplasm of one cell to its opposing neighbours. They are found in almost all vertebrate cell types, and somewhat similar proteins have been cloned from plant species. Invertebrates utilise a different family of molecules, innexins, that share a similar predicted secondary structure to the vertebrate connexins, but have no sequence identity to them [PUBMED:9769729].

Vertebrate gap junction channels are thought to participate in diverse biological functions. For instance, in the heart they permit the rapid cell-cell transfer of action potentials, ensuring coordinated contraction of the cardiomyocytes. They are also responsible for neurotransmission at specialised 'electrical' synapses. In non-excitable tissues, such as the liver, they may allow metabolic cooperation between cells. In the brain, glial cells are extensively-coupled by gap junctions; this allows waves of intracellular Ca2+ to propagate through nervous tissue, and may contribute to their ability to spatially-buffer local changes in extracellular K+ concentration [PUBMED:7685944].

The connexin protein family is encoded by at least 13 genes in rodents, with many homologues cloned from other species. They show overlapping tissue expression patterns, most tissues expressing more than one connexin type. Their conductances, permeability to different molecules, phosphorylation and voltage-dependence of their gating, have been found to vary. Possible communication diversity is increased further by the fact that gap junctions may be formed by the association of different connexin isoforms from apposing cells. However, in vitro studies have shown that not all possible combinations of connexins produce active channels [PUBMED:8811187, PUBMED:8608591].

Hydropathy analysis predicts that all cloned connexins share a common transmembrane (TM) topology. Each connexin is thought to contain 4 TM domains, with two extracellular and three cytoplasmic regions. This model has been validated for several of the family members by in vitro biochemical analysis. Both N- and C-termini are thought to face the cytoplasm, and the third TM domain has an amphipathic character, suggesting that it contributes to the lining of the formed-channel. Amino acid sequence identity between the isoforms is ~50-80%, with the TM domains being well conserved. Both extracellular loops contain characteristically conserved cysteine residues, which likely form intramolecular disulphide bonds. By contrast, the single putative intracellular loop (between TM domains 2 and 3) and the cytoplasmic C terminus are highly variable among the family members. Six connexins are thought to associate to form a hemi-channel, or connexon. Two connexons then interact (likely via the extracellular loops of their connexins) to form the complete gap junction channel.

 
       NH2-***        ***        *************-COOH
             **     **   **      **
             **    **     **    **   Cytoplasmic
          ---**----**-----**----**----------------
             **    **     **    **   Membrane
             **    **     **    **
          ---**----**-----**----**----------------
             **    **     **    **   Extracellular
              **  **       **  **
                **           **

Two sets of nomenclature have been used to identify the connexins. The first, and most commonly used, classifies the connexin molecules according to molecular weight, such as connexin43 (abbreviated to Cx43), indicating a connexin of molecular weight close to 43kDa. However, studies have revealed cases where clear functional homologues exist across species that have quite different molecular masses; therefore, an alternative nomenclature was proposed based on evolutionary considerations, which divides the family into two major subclasses, alpha and beta, each with a number of members [PUBMED:1320430]. Due to their ubiquity and overlapping tissue distributions, it has proved difficult to elucidate the functions of individual connexin isoforms. To circumvent this problem, particular connexin-encoding genes have been subjected to targeted-disruption in mice, and the phenotype of the resulting animals investigated. Around half the connexin isoforms have been investigated in this manner [PUBMED:9861669]. Further insight into the functional roles of connexins has come from the discovery that a number of human diseases are caused by mutations in connexin genes. For instance, mutations in Cx32 give rise to a form of inherited peripheral neuropathy called X-linked dominant Charcot-Marie-Tooth disease [PUBMED:7570999]. Similarly, mutations in Cx26 are responsible for both autosomal recessive and dominant forms of nonsyndromic deafness, a disorder characterised by hearing loss, with no apparent effects on other organ systems.

Gap junction alpha-1 protein (also called connexin43, or Cx43) is a connexin of 381 amino acid residues (human isoform) that is widely expressed in several organs and cell types, and is the principal gap junction protein of the heart. Characterisation of genetically-engineered mice that lack Cx43, and also of human patients that have spontaneously-occurring mutations in the gene encoding it (GJA1), suggest Cx43 is essential for the development of normal cardiac architecture and ventricular conduction. Mice lacking Cx43 survive to term but die shortly after birth. They have cardiac malformations that lead to the obstruction of the pulmonary artery, leading to neonatal cyanosis, and subsequent death. This phenotype is reminiscent of some forms of stenosis of the pulmonary artery. Human subjects with visceroatrial heterotaxia (a heart disorder characterised by arterial defects), have been found to have points mutations in the Cx43-encoding gene, as a result of which a potential phosphorylation site within the C terminus is disrupted. Consequently, although these mutant Cx43 molecules still form functional gap junction channels, their response to protein kinase activation is impaired.

This domain is found in the C-terminal region of these proteins.

Domain organisation

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Alignments

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We make a range of alignments for each Pfam-A family. You can see a description of each above. You can view these alignments in various ways but please note that some types of alignment are never generated while others may not be available for all families, most commonly because the alignments are too large to handle.

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  Seed
(3)
Full
(90)
Representative proteomes NCBI
(85)
Meta
(0)
RP15
(1)
RP35
(3)
RP55
(8)
RP75
(24)
Alignment:
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  Seed
(3)
Full
(90)
Representative proteomes NCBI
(85)
Meta
(0)
RP15
(1)
RP35
(3)
RP55
(8)
RP75
(24)
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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:

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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

This section shows the detailed information about the Pfam family. You can see the definitions of many of the terms in this section in the glossary and a fuller explanation of the scoring system that we use in the scores section of the help pages.

Curation View help on the curation process

Seed source: PRINTS
Previous IDs: none
Type: Family
Author: Griffiths-Jones SR
Number in seed: 3
Number in full: 90
Average length of the domain: 20.00 aa
Average identity of full alignment: 92 %
Average coverage of the sequence by the domain: 5.88 %

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 37.0 37.0
Noise cut-off 23.6 22.8
Model length: 20
Family (HMM) version: 8
Download: download the raw HMM for this family

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 Connexin43 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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