{PDOC00341}
{PS00407; CONNEXINS_1}
{PS00408; CONNEXINS_2}
{BEGIN}
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* Connexins signatures *
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Gap junctions [1] are specialized regions of the plasma membrane which consist
of closely  packed  pairs  of  transmembrane  channels, the connexons, through
which small molecules diffuse from a cell to a neighboring cell. Each connexon
is composed  of  an  hexamer  of  an  integral membrane protein which is often
referred to  as  connexin. In a given species there are a number of different,
yet structurally  related,  tissue specific, forms of connexins.  The types of
connexins which are currently known are listed below.

 - Connexin 56   (Cx56).
 - Connexin 50   (Cx50)   (lens fiber protein MP70).
 - Connexin 46   (Cx46)   (alpha-3).
 - Connexin 45   (Cx45)   (alpha-6).
 - Connexin 43   (Cx43)   (alpha-1).
 - Connexin 40   (Cx40)   (alpha-5).
 - Connexin 38   (Cx38)   (alpha-2).
 - Connexin 37   (Cx37)   (alpha-4).
 - Connexin 33   (Cx33)   (alpha-7).
 - Connexin 32   (Cx32)   (beta-1).
 - Connexin 31.1 (Cx31.1) (beta-4).
 - Connexin 31   (Cx31)   (beta-3).
 - Connexin 30.3 (Cx30.3) (beta-5).
 - Connexin 26   (Cx26)   (beta-2).

Structurally the connexins  consist of a  short cytoplasmic N-terminal domain,
followed by four  transmembrane  segments  that delimit  two extracellular and
one cytoplasmic loops; the C-terminal domain is cytoplasmic  and its length is
variable  (from 20 residues in Cx26  to  260 residues in Cx56).  The schematic
representation of this structure is shown below.

       NH2-***        ***          *************-COOH
             **     **   **      **
             **    **     **    **   Cytoplasmic
          ---**----**-----**----**----------------
             **    **     **    **   Membrane
             **    **     **    **
          ---**----**-----**----**----------------
             **    **     **    **   Extracellular
              **  **       **  **
                **           **

The sequences of the two extracellular loops are well conserved. In both loops
there are three conserved cysteines which are involved in disulfide bonds.  We
have built signature patterns from each of these two loop regions.

-Consensus pattern: C-[DNH]-[TL]-x-[QT]-P-G-C-x(2)-[VAIL]-C-[FY]-D
                    [The 3 C's are involved in disulfide bonds]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Consensus pattern: C-x(3,4)-P-C-x(2,3)-[LIVMTA]-[DENT]-C-[FYN]-[LIVMQ]-[SA]-
                    [KRH]-P
                    [The 3 C's are involved in disulfide bonds]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Last update: April 2006 / Patterns revised.

[ 1] Goodenough D.A., Goliger J.A., Paul D.L.
     "Connexins, connexons, and intercellular communication."
     Annu. Rev. Biochem. 65:475-502(1996).
     PubMed=8811187; DOI=10.1146/annurev.bi.65.070196.002355

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