PROSITE documentation PDOC00197
Crystallins beta and gamma 'Greek key' motif profile


Crystallins are the dominant structural components of the eye lens. Among the different type of crystallins, the β and γ crystallins form a family of related proteins [1,2]. Structurally, β and γ 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' motif, composed of four antiparallel β-strands: a, b, c, and d (see <PDB:1A45>).

Apart from the different types of β and γ 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].
  • Epidermis differenciation-specific protein (EDSP or ep37) of the amphibian Cynops pyrrhogaster.
  • Mammalian absent in melanoma 1 protein (AIM1). It contains 12 'Greek key' motifs.

β/γ 'Greek key' motifs may be further classified as A- or B-type. Vertebrate members of the β/γ superfamily conform to an ABAB motif pattern. B-type motifs are the most highly conserved and form most of the contacts between domains. In protein S, the order of motifs is reversed to BABA, suggesting a separate history of duplication events [4].

The profile we developed for this family of proteins covers the entire 'Greek key' motif.

Expert(s) to contact by email:

Wistow G.

Last update:

July 2003 / Pattern removed, profile added and text revised.


Technical section

PROSITE method (with tools and information) covered by this documentation:

CRYSTALLIN_BETA_GAMMA, PS50915; Crystallins beta and gamma 'Greek key' motif profile  (MATRIX)


1AuthorsLubsen N.H. Aarts H.J.M. Schoenmakers J.G.
TitleThe evolution of lenticular proteins: the beta- and gamma-crystallin super gene family.
SourceProg. Biophys. Mol. Biol. 51:47-76(1988).
PubMed ID3064189

2AuthorsWistow G.J. Piatigorsky J.
TitleLens crystallins: the evolution and expression of proteins for a highly specialized tissue.
SourceAnnu. Rev. Biochem. 57:479-504(1988).
PubMed ID3052280

3AuthorsWistow G.
TitleEvolution of a protein superfamily: relationships between vertebrate lens crystallins and microorganism dormancy proteins.
SourceJ. Mol. Evol. 30:140-145(1990).
PubMed ID2107329

4AuthorsRay M.E. Wistow G. Su Y.A. Meltzer P.S. Trent J.M.
TitleAIM1, a novel non-lens member of the betagamma-crystallin superfamily, is associated with the control of tumorigenicity in human malignant melanoma.
SourceProc. Natl. Acad. Sci. U.S.A. 94:3229-3234(1997).
PubMed ID9096375

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