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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. 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-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.  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: NONE.

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

-Last update: June 1994 / Pattern and text revised.

[ 1] Hynes R.O.
     Cell 48:549-554(1987).
[ 2] Albelda S.M., Buck C.A.
     FASEB J. 4:2868-2880(1990).