Integrin alpha chain (IPR000413)
Short name: Integrin_alpha
Overlapping homologous superfamilies
- Integrin alpha, N-terminal (IPR028994)
Integrins are the major metazoan receptors for cell adhesion to extracellular matrix proteins and, in vertebrates, also play important roles in certain cell-cell adhesions, make transmembrane connections to the cytoskeleton and activate many intracellular signalling pathways [PMID: 12297042, PMID: 12361595]. An integrin receptor is a heterodimer composed of alpha and beta subunits. Each subunit crosses the membrane once, with most of the polypeptide residing in the extracellular space, and has two short cytoplasmic domains. Some members of this family have EGF repeats at the C terminus and also have a vWA domain inserted within the integrin domain at the N terminus.
Most integrins recognise relatively short peptide motifs, and in general require an acidic amino acid to be present. Ligand specificity depends upon both the alpha and beta subunits [PMID: 12234368]. There are at least 18 types of alpha and 8 types of beta subunits recognised in humans [PMID: 14689578]. Each alpha subunit tends to associate only with one type of beta subunit, but there are exceptions to this rule [PMID: 2467745]. Each association of alpha and beta subunits has its own binding specificity and signalling properties. Many integrins require activation on the cell surface before they can bind ligands. Integrins frequently intercommunicate, and binding at one integrin receptor activate or inhibit another.
Some alpha subunits are cleaved post- translationally to produce a heavy and a light chain linked by a disulphide bond [PMID: 3028640, PMID: 2199285]. Integrin alpha chains share a conserved sequence which is found at the beginning of the cytoplasmic domain, just after the end of the transmembrane region. Within the N-terminal domain of alpha subunits, seven sequence repeats, each of approximately 60 amino acids, have been found [PMID: 3327687]. It has been predicted that these repeats assume the beta-propeller fold. The domains contain seven four-stranded beta-sheets arranged in a torus around a pseudosymmetry axis [PMID: 8990162]. Integrin ligands and a putative Mg2+ ion are predicted to bind to the upper face of the propeller, in a manner analogous to the way in which the trimeric G-protein beta subunit (G beta) (which also has a beta-propeller fold) binds the G protein alpha subunit [PMID: 8990162].
Integrin cytoplasmic domains are normally less than 50 amino acids in length, with the beta-subunit sequences exhibiting greater homology to each other than the alpha-subunit sequences [PMID: 12826403]. This is consistent with current evidence that the beta subunit is the principal site for binding of cytoskeletal and signalling molecules, whereas the alpha subunit has a regulatory role. The first ten residues of the alpha-subunit cytoplasmic domain appear to form an alpha helix that is terminated by a proline residue. The remainder of the domain is highly acidic in nature and this loops back to contact the membrane-proximal lysine anchor residue.
- PR01185 (INTEGRINA)