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10  structures 690  species 0  interactions 2358  sequences 45  architectures

Family: B2-adapt-app_C (PF09066)

Summary: Beta2-adaptin appendage, C-terminal sub-domain

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This is the Wikipedia entry entitled "B2-adapt-app C". More...

B2-adapt-app C Edit Wikipedia article

PDB 1e42 EBI.jpg
beta2-adaptin appendage domain, from clathrin adaptor ap2
Symbol B2-adapt-app_C
Pfam PF09066
InterPro IPR015151
SCOP 1e42

The C-terminal domain of Beta2-adaptin is a protein domain is involved in cell trafficking by aiding import and export of substances in and out of the cell.


This is an adaptor protein which helps the formation of a clathrin coat around a vesicle.


This entry represents a subdomain of the appendage (ear) domain of beta-adaptin from AP clathrin adaptor complexes. This domain has a three-layer arrangement, alpha-beta-alpha, with a bifurcated antiparallel beta-sheet.[1] This domain is required for binding to clathrin, and its subsequent polymerisation. Furthermore, a hydrophobic patch present in the domain also binds to a subset of D-phi-F/W motif-containing proteins that are bound by the alpha-adaptin appendage domain (epsin, AP180, eps15).[2]

Cell trafficking

Proteins synthesized on the ribosome and processed in the endoplasmic reticulum are transported from the Golgi apparatus to the trans-Golgi network (TGN), and from there via small carrier vesicles to their final destination compartment. These vesicles have specific coat proteins (such as clathrin or coatomer) that are important for cargo selection and direction of transport.[3] Clathrin coats contain both clathrin (acts as a scaffold) and adaptor complexes that link clathrin to receptors in coated vesicles. Clathrin-associated protein complexes are believed to interact with the cytoplasmic tails of membrane proteins, leading to their selection and concentration. The two major types of clathrin adaptor complexes are the heterotetrameric adaptor protein (AP) complexes, and the monomeric GGA (Golgi-localising, Gamma-adaptin ear domain homology, ARF-binding proteins) adaptors.[4][5]

AP (adaptor protein) complexes are found in coated vesicles and clathrin-coated pits. AP complexes connect cargo proteins and lipids to clathrin at vesicle budding sites, as well as binding accessory proteins that regulate coat assembly and disassembly (such as AP180, epsins and auxilin). There are different AP complexes in mammals. AP1 is responsible for the transport of lysosomal hydrolases between the TGN and endosomes.[6] AP2 associates with the plasma membrane and is responsible for endocytosis.[7] AP3 is responsible for protein trafficking to lysosomes and other related organelles.[8] AP4 is less well characterised. AP complexes are heterotetramers composed of two large subunits (adaptins), a medium subunit (mu) and a small subunit (sigma). For example, in AP1 these subunits are gamma-1-adaptin, beta-1-adaptin, mu-1 and sigma-1, while in AP2 they are alpha-adaptin, beta-2-adaptin, mu-2 and sigma-2. Each subunit has a specific function. Adaptins recognise and bind to clathrin through their hinge region (clathrin box), and recruit accessory proteins that modulate AP function through their C-terminal ear (appendage) domains. Mu recognises tyrosine-based sorting signals within the cytoplasmic domains of transmembrane cargo proteins.[9] One function of clathrin and AP2 complex-mediated endocytosis is to regulate the number of GABA(A) receptors available at the cell surface .[10]

More information about these proteins can be found at Protein of the Month: Clathrin .


  1. ^ Traub LM, Downs MA, Westrich JL, Fremont DH (August 1999). "Crystal structure of the alpha appendage of AP-2 reveals a recruitment platform for clathrin-coat assembly". Proc. Natl. Acad. Sci. U.S.A. 96 (16): 8907–12. PMC 17706Freely accessible. PMID 10430869. doi:10.1073/pnas.96.16.8907. 
  2. ^ Owen DJ, Vallis Y, Pearse BM, McMahon HT, Evans PR (August 2000). "The structure and function of the beta 2-adaptin appendage domain". EMBO J. 19 (16): 4216–27. PMC 302036Freely accessible. PMID 10944104. doi:10.1093/emboj/19.16.4216. 
  3. ^ McMahon HT, Mills IG (August 2004). "COP and clathrin-coated vesicle budding: different pathways, common approaches". Curr. Opin. Cell Biol. 16 (4): 379–91. PMID 15261670. doi:10.1016/ 
  4. ^ Voglmaier SM, Edwards RH (June 2007). "Do different endocytic pathways make different synaptic vesicles?". Curr. Opin. Neurobiol. 17 (3): 374–80. PMID 17449236. doi:10.1016/j.conb.2007.04.002. 
  5. ^ Boehm M, Bonifacino JS (October 2001). "Adaptins: the final recount". Mol. Biol. Cell. 12 (10): 2907–20. PMC 60144Freely accessible. PMID 11598180. doi:10.1091/mbc.12.10.2907. 
  6. ^ Touz MC, Kulakova L, Nash TE (July 2004). "Adaptor protein complex 1 mediates the transport of lysosomal proteins from a Golgi-like organelle to peripheral vacuoles in the primitive eukaryote Giardia lamblia". Mol. Biol. Cell. 15 (7): 3053–60. PMC 452563Freely accessible. PMID 15107467. doi:10.1091/mbc.E03-10-0744. 
  7. ^ Conner SD, Schmid SL (September 2003). "Differential requirements for AP-2 in clathrin-mediated endocytosis". J. Cell Biol. 162 (5): 773–9. PMC 2172816Freely accessible. PMID 12952931. doi:10.1083/jcb.200304069. 
  8. ^ Gupta SN, Kloster MM, Rodionov DG, Bakke O (June 2006). "Re-routing of the invariant chain to the direct sorting pathway by introduction of an AP3-binding motif from LIMP II". Eur. J. Cell Biol. 85 (6): 457–67. PMID 16542748. doi:10.1016/j.ejcb.2006.02.001. 
  9. ^ Haucke V, Wenk MR, Chapman ER, Farsad K, De Camilli P (November 2000). "Dual interaction of synaptotagmin with mu2- and alpha-adaptin facilitates clathrin-coated pit nucleation". EMBO J. 19 (22): 6011–9. PMC 305843Freely accessible. PMID 11080148. doi:10.1093/emboj/19.22.6011. 
  10. ^ Kanematsu T, Fujii M, Mizokami A, Kittler JT, Nabekura J, Moss SJ, Hirata M (May 2007). "Phospholipase C-related inactive protein is implicated in the constitutive internalization of GABAA receptors mediated by clathrin and AP2 adaptor complex". J. Neurochem. 101 (4): 898–905. PMID 17254016. doi:10.1111/j.1471-4159.2006.04399.x. 

This article incorporates text from the public domain Pfam and InterPro IPR015151

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Beta2-adaptin appendage, C-terminal sub-domain Provide feedback

Members of this family adopt a structure consisting of a 5 stranded beta-sheet, flanked by one alpha helix on the outer side, and by two alpha helices on the inner side. This domain is required for binding to clathrin, and its subsequent polymerisation. Furthermore, a hydrophobic patch present in the domain also binds to a subset of D-phi-F/W motif-containing proteins that are bound by the alpha-adaptin appendage domain (epsin, AP180, eps15) [1].

Literature references

  1. Owen DJ, Vallis Y, Pearse BM, McMahon HT, Evans PR; , EMBO J. 2000;19:4216-4227.: The structure and function of the beta 2-adaptin appendage domain. PUBMED:10944104 EPMC:10944104

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External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR015151

This entry represents a subdomain of the appendage (ear) domain of beta-adaptin. This domain has a three-layer arrangement, alpha-beta-alpha, with a bifurcated antiparallel beta-sheet [ PUBMED:10430869 ]. This domain is required for binding to clathrin, and its subsequent polymerisation. Furthermore, a hydrophobic patch present in the domain also binds to a subset of D-phi-F/W motif-containing proteins that are bound by the alpha-adaptin appendage domain (epsin, AP180, eps15) [ PUBMED:10944104 ].

Gene Ontology

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Domain organisation

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Pfam Clan

This family is a member of clan APCOP-app_sub (CL0545), which has the following description:

This superfamily is characterised by subdomains from the clathrin and coatomer appendages. The superfamily possesses a single protein/protein interaction site that in yeast binds to the ARFGAP Glo3p, and in mammalian gamma-COP binds to a Glo3p orthologue, ARFGAP2 [1].

The clan contains the following 5 members:

Alpha_adaptin_C AP4E_app_platf B2-adapt-app_C Coatomer_b_Cpla Coatomer_g_Cpla


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Seed source: pdb_1e42
Previous IDs: none
Type: Domain
Sequence Ontology: SO:0000417
Author: Sammut SJ
Number in seed: 88
Number in full: 2358
Average length of the domain: 106.60 aa
Average identity of full alignment: 33 %
Average coverage of the sequence by the domain: 13.00 %

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HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 57096847 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 22.6 22.6
Trusted cut-off 22.7 22.6
Noise cut-off 22.4 22.4
Model length: 112
Family (HMM) version: 12
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Archea Archea Eukaryota Eukaryota
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Viroids Viroids Unclassified sequence Unclassified sequence


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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 B2-adapt-app_C domain has been found. There are 10 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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