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1401  structures 1607  species 0  interactions 31597  sequences 413  architectures

Family: Actin (PF00022)

Summary: Actin

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This is the Wikipedia entry entitled "Actin". More...

Actin Edit Wikipedia article

Actin is a protein important for cell movements. It is expressed in all body cells, but especially in muscle cells. Actin can polymerize into microfilament, which are essential for the cytoskeleton, for cell motility, and for contraction of the cell during cell division.

Together with myosin filaments, actin provides the mechanism for muscle contraction, utilizing energy from ATP.

This page is based on a Wikipedia article. The text is available under the Creative Commons Attribution/Share-Alike License.

This tab holds the annotation information that is stored in the Pfam database. As we move to using Wikipedia as our main source of annotation, the contents of this tab will be gradually replaced by the Wikipedia tab.

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No Pfam abstract.

Literature references

  1. Schutt CE, Myslik JC, Rozycki MD, Goonesekere NC, Lindberg U; , Nature 1993;365:810-816.: The structure of crystalline profilin-beta-actin. PUBMED:8413665 EPMC:8413665

  2. Sheterline P, Clayton J, Sparrow J; , Protein Profile 1995;2:1-103.: Actin PUBMED:8548558 EPMC:8548558

Internal database links

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR004000

Actin [ PUBMED:1388079 , PUBMED:8448030 ] is a ubiquitous protein involved in the formation of filaments that are major components of the cytoskeleton. These filaments interact with myosin to produce a sliding effect, which is the basis of muscular contraction and many aspects of cell motility, including cytokinesis. Each actin protomer binds one molecule of ATP and has one high affinity site for either calcium or magnesium ions, as well as several low affinity sites. Actin exists as a monomer in low salt concentrations, but filaments form rapidly as salt concentration rises, with the consequent hydrolysis of ATP. Actin from many sources forms a tight complex with deoxyribonuclease (DNase I) although the significance of this is still unknown. The formation of this complex results in the inhibition of DNase I activity, and actin loses its ability to polymerise. It has been shown that an ATPase domain of actin shares similarity with ATPase domains of hexokinase and hsp70 proteins [ PUBMED:1828889 , PUBMED:1323828 ].

In vertebrates there are three groups of actin isoforms: alpha, beta and gamma. The alpha actins are found in muscle tissues and are a major constituent of the contractile apparatus. The beta and gamma actins co-exists in most cell types as components of the cytoskeleton and as mediators of internal cell motility. In plants there are many isoforms which are probably involved in a variety of functions such as cytoplasmic streaming, cell shape determination, tip growth, graviperception, cell wall deposition, etc.

Recently some divergent actin-like proteins have been identified in several species. These proteins include centractin (actin-RPV) from mammals, fungi yeast ACT5, Neurospora crassa ro-4 and Pneumocystis carinii, which seems to be a component of a multi-subunit centrosomal complex involved in microtubule based vesicle motility (this subfamily is known as ARP1); ARP2 subfamily, which includes chicken ACTL, Saccharomyces cerevisiae ACT2, Drosophila melanogaster 14D and Caenorhabditis elegans actC; ARP3 subfamily, which includes actin 2 from mammals, Drosophila 66B, yeast ACT4 and Schizosaccharomyces pombe act2; and ARP4 subfamily, which includes yeast ACT3 and Drosophila 13E.

Domain organisation

Below is a listing of the unique domain organisations or architectures in which this domain is found. More...

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Pfam Clan

This family is a member of clan Actin_ATPase (CL0108), which has the following description:

The actin-like ATPase domain forms an alpha/beta canonical fold. The domain can be subdivided into 1A, 1B, 2A and 2B subdomains. Subdomains 1A and 1B share the same RNAseH-like fold (a five-stranded beta-sheet decorated by a number of alpha-helices). Domains 1A and 2A are conserved in all members of this superfamily, whereas domain 1B and 2B have a variable structure and are even missing from some homologues [1]. Within the actin-like ATPase domain the ATP-binding site is highly conserved. The phosphate part of the ATP is bound in a cleft between subdomains 1A and 2A, whereas the adenosine moiety is bound to residues from domains 2A and 2B[1].

The clan contains the following 34 members:

Acetate_kinase Actin Actin_micro ALP_N AnmK BcrAD_BadFG Carbam_trans_N DDR DUF1464 DUF2229 EutA FGGY_C FGGY_N FtsA Fumble GDA1_CD39 Glucokinase Hexokinase_1 Hexokinase_2 HGD-D HSP70 Hydant_A_N Hydantoinase_A HypF_C MreB_Mbl MutL Pan_kinase PilM_2 Ppx-GppA RACo_C_ter ROK StbA T2SSL TsaD


We store a range of different sequence alignments for families. As well as the seed alignment from which the family is built, we provide the full alignment, generated by searching the sequence database (reference proteomes) using the family HMM. We also generate alignments using four representative proteomes (RP) sets and the UniProtKB sequence database. More...

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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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Representative proteomes UniProt

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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.

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

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HMM logos is one way of visualising profile HMMs. Logos provide a quick overview of the properties of an HMM in a graphical form. You can see a more detailed description of HMM logos and find out how you can interpret them here. More...


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.

Note: You can also download the data file for the tree.

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: Prosite
Previous IDs: actin;
Type: Family
Sequence Ontology: SO:0100021
Author: Sonnhammer ELL
Number in seed: 24
Number in full: 31597
Average length of the domain: 323.5 aa
Average identity of full alignment: 29 %
Average coverage of the sequence by the domain: 83.21 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 61295632 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 27.0 27.0
Trusted cut-off 27.0 27.0
Noise cut-off 26.9 26.9
Model length: 385
Family (HMM) version: 22
Download: download the raw HMM for this family

Species distribution

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Colour assignments

Archea Archea Eukaryota Eukaryota
Bacteria Bacteria Other sequences Other sequences
Viruses Viruses Unclassified Unclassified
Viroids Viroids Unclassified sequence Unclassified sequence


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This visualisation provides a simple graphical representation of the distribution of this family across species. You can find the original interactive tree in the adjacent tab. More...

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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 Actin domain has been found. There are 1401 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 sequence.

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AlphaFold Structure Predictions

The list of proteins below match this family and have AlphaFold predicted structures. Click on the protein accession to view the predicted structure.

Protein Predicted structure External Information
A0A044QUC6 View 3D Structure Click here
A0A044R6W7 View 3D Structure Click here
A0A044S924 View 3D Structure Click here
A0A044SKC5 View 3D Structure Click here
A0A044SYL7 View 3D Structure Click here
A0A044TP52 View 3D Structure Click here
A0A044UZ44 View 3D Structure Click here
A0A044VI25 View 3D Structure Click here
A0A077YW41 View 3D Structure Click here
A0A077YWW9 View 3D Structure Click here
A0A077YZB7 View 3D Structure Click here
A0A077Z273 View 3D Structure Click here
A0A077Z4G1 View 3D Structure Click here
A0A077Z5X0 View 3D Structure Click here
A0A077Z6U3 View 3D Structure Click here
A0A077Z8W4 View 3D Structure Click here
A0A077Z9I9 View 3D Structure Click here
A0A077ZE37 View 3D Structure Click here
A0A077ZFF5 View 3D Structure Click here
A0A077ZFF7 View 3D Structure Click here
A0A0D2DFA3 View 3D Structure Click here
A0A0D2DTC4 View 3D Structure Click here
A0A0D2EMI3 View 3D Structure Click here
A0A0D2EXD6 View 3D Structure Click here
A0A0D2F1L8 View 3D Structure Click here
A0A0D2GQJ0 View 3D Structure Click here
A0A0D2GSQ8 View 3D Structure Click here
A0A0D2GWL4 View 3D Structure Click here
A0A0D2GZE2 View 3D Structure Click here
A0A0D2HNS6 View 3D Structure Click here
A0A0G2KAE0 View 3D Structure Click here
A0A0H5S0H8 View 3D Structure Click here
A0A0H5S4Y1 View 3D Structure Click here
A0A0H5SER1 View 3D Structure Click here
A0A0J9XUT5 View 3D Structure Click here
A0A0K0DSN4 View 3D Structure Click here
A0A0K0DTP8 View 3D Structure Click here
A0A0K0DWT5 View 3D Structure Click here
A0A0K0DXX5 View 3D Structure Click here
A0A0K0EE83 View 3D Structure Click here