{PDOC00215}
{PS00242; INTEGRIN_ALPHA}
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* Integrins alpha chain signature *
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Integrins [1,2] are a large family of cell surface receptors that mediate cell
to cell as well as cell to matrix adhesion. Some integrins recognize the R-G-D
sequence in their extracellular matrix protein ligand. Structurally, integrins
consist of a dimer of an alpha and a beta chain.  Each  subunit  has  a  large
N-terminal extracellular domain followed by a transmembrane domain and a short
C-terminal cytoplasmic  region.    Some    alpha  subunits   are cleaved post-
translationally to produce  a  heavy  and a  light chain linked by a disulfide
bond. The  sequence  of  a  number  of  alpha chains has been obtained and are
listed below:

 - The alpha-1 chain (VLA-1) (CD49a)  which,  with the beta-1 chain, acts as a
   receptor for laminin and collagen.
 - The alpha-2 chain (VLA-2) (CD49b)  which,  with the beta-1 chain, acts as a
   receptor that binds collagen.
 - The alpha-3 chain (VLA-3) (Galactoprotein B3).
 - The alpha-4 chain (VLA-4) (CD49d)  which,  with the beta-1 chain, interacts
   with vascular cell adhesion protein 1 (VCAM-1).
 - The alpha-5 chain (VLA-5) (CD49e) which,  with  the beta-1 chain,  forms  a
   receptor specific to fibronectin.
 - The alpha-6 chain (VLA-6) which,  with  the beta-1  chain, forms a platelet
   laminin receptor.
 - The  alpha-7  chain which, with the beta-1 chain, forms a skeletal myoblast
   laminin receptor.
 - The alpha-8 chain which, with the  beta-1 chain  plays  a  possible role in
   cell-cell interactions during axon-growth and fasciculation.
 - The alpha-L chain (LFA-1) (CD11a)  which, with the beta-2 chain,  interacts
   with intercellular adhesion molecule 1 (ICAM-1).
 - The alpha-M chain (MAC-1) (CD11b)  which, with  the beta-2 chain, forms the
   receptor for the iC3b fragment of the third complement component.
 - The alpha-X chain (p150,95) (CD11c) which, with  the beta-2 chain, probably
   forms a receptor for the iC3b fragment of the third complement component.
 - The alpha-V chain (CD51) which,  with  the  beta-3 chain,  forms a receptor
   that binds vitronectin.
 - The alpha-IIB chain (CD41) (also known as platelet glycoprotein IIb) which,
   with  the beta-3 chain, forms  a  receptor  which  binds  VWF,  fibrinogen,
   fibronectin, and vitronectin.
 - The Drosophila position-specific antigen 2 alpha chain (PS2).
 - Caenorhabditis elegans hypothetical proteins F54F2.1 and F54G8.3.

All these  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.   This   motif   is  probably  involved  in  heterodimer
association and  may  lock the heterodimer into a low affinity conformation in
the abscence  of  activating  signals. We have used this conserved region as a
signature pattern.

-Consensus pattern: [FYWS]-[RK]-x-G-F-F-x-R
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: 3.

-Note: In position 7 of  the  pattern all vertebrate integrins have Lys, while
 Drosophila PS2 has Asn.

-Last update: December 2001 / Text revised.

[ 1] Hynes R.O.
     "Integrins: a family of cell surface receptors."
     Cell 48:549-554(1987).
     PubMed=3028640
[ 2] Albelda S.M., Buck C.A.
     "Integrins and other cell adhesion molecules."
     FASEB J. 4:2868-2880(1990).
     PubMed=2199285

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