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* Crystallins beta and gamma 'Greek key' motif signature *
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Crystallins are  the dominant structural components of the eye lens. Among the
different type of crystallins, the beta and gamma crystallins form a family of
related  proteins [1,2]. Structurally, beta and gamma crystallins are composed
of two similar domains which, in turn, are each composed of two similar motifs
with the  two domains  connected  by  a  short connecting peptide. Each motif,
which  is about  forty  amino  acid  residues long, is folded in a distinctive
'Greek key' pattern.

Apart from  the different types  of  beta and  gamma crystallins, this  family
also includes the following proteins:

 - Two related proteins  from  the  sporulating  bacterium Myxococcus xanthus:
   protein S, a calcium-binding protein  that  forms a major part of the spore
   coat, and a close homolog of protein S.
 - Spherulin 3a from the slime mold  Physarum polycephalum.  Spherulin 3a is a
   development specific  protein  synthesized in  response to various kinds of
   stress leading to encystment and dormancy.  The  sequence  of  Spherulin 3a
   consists of two 'Greek key' motifs [3].

The pattern we developed for this family of proteins span positions 3 to 18 of
the Greek-key motif and includes three conserved positions which are important
for the  structural integrity  of the motif.  These are the conserved aromatic
residues in positions 6 and 11 of the motif and the glycine in position 13.

-Consensus pattern: [LIVMFYWA]-x-{DEHRKSTP}-[FY]-[DEQHKY]-x(3)-[FY]-x-G-x(4)-
                    [LIVMFCST]
-Sequences known to belong to this class detected by the pattern: ALL.    In a
 few cases the pattern will fail to detect one of the four motifs.
-Other sequence(s) detected in SWISS-PROT: 122, but in all these sequences the
 pattern is found only ONCE.
-Last update: April 1990 / Text revised.

[ 1] Lubsen N.H., Aarts H.J.M., Schoenmakers J.G.G.
     Prog. Biophys. Mol. Biol. 51:47-76(1988).
[ 2] Wistow G.J., Piatigorsky J.
     Annu. Rev. Biochem. 57:479-504(1988).
[ 3] Wistow G.
     J. Mol. Evol. 30:140-145(1990).