{PDOC00535}
{PS00612; OSTEONECTIN_1}
{PS00613; OSTEONECTIN_2}
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*********************************
* Osteonectin domain signatures *
*********************************

The following extracellular proteins  contain, in their C-terminal section,  a
domain of  about 240 amino acids which is highly conserved [1]. These proteins
are:

 - SPARC  (also known as Osteonectin or BM-40), a glycoprotein that appears to
   regulate cell growth through interactions with the extracellular matrix and
   cytokines. It binds calcium and copper, several types of collagen, albumin,
   thrombospondin, PDGF  and  cell  membranes.  There  are two calcium binding
   sites; a acidic domain that binds 5 to 8 Ca++ with a low affinity and a EF-
   hand loop that binds a Ca++ ion with a high affinity. SPARC is expressed at
   high levels in tissues undergoing morphogenesis, remodeling and repair.
 - SC1, a mammalian brain extracellular matrix protein.
 - QR1, an avian protein, specifically expressed in the neuroretina.

This domain    has  a N-terminal section of about 90 residues that contains 11
conserved cysteines, a  central  section  that is probably in an alpha-helical
conformation, and a C-terminal section that contains two EF-hand type calcium-
binding regions   [2]  and  three  conserved  cysteines.    This  topology  is
schematically represented below.

                                                                     +----+
                                                                     |    |
 xCxCxCxxCCxCxxxCxxCxCxxxxxCxCxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx<Ca>xCxxC<Ca>Cxx
  ***********                   ***

'C' : conserved cysteines involved in disulfide bonds.
'Ca': EF-hand region (see <PDOC00018>).
'*' : position of the patterns.

We developed two signature   patterns for  this  domain. One is located in the
C-terminal  cysteine-rich  section, the  other  consists in a highly conserved
stretch of 11 residues in the central section.

-Consensus pattern: C-x-[DNS]-x(2)-C-x(2)-G-[KRH]-x-C-x(6,7)-P-x-C-x-C-x(3,5)-
                    C-P
                    [The 6 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: F-P-x-R-[IM]-x-D-W-L-x-[NQ]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: NONE.

-Expert(s) to contact by email:
           Maurer P.; maurer2@urz.unibas.ch

-Last update: December 2004 / Pattern and text revised.

[ 1] Lane T.F., Sage E.H.
     "The biology of SPARC, a protein that modulates cell-matrix
     interactions."
     FASEB J. 8:163-173(1994).
     PubMed=8119487
[ 2] Hohenester E., Maurer P., Hohenadl C., Timpl R., Jansonius J.N.,
     Engel J.
     "Structure of a novel extracellular Ca(2+)-binding module in BM-40."
     Nat. Struct. Biol. 3:67-73(1996).
     PubMed=8548457

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