The CSPG (chondroitin sulfate proteoglycan) repeat is a cadherin-like and tumor-relevant protein module which is thought to mediate interactions between cells and the extracellular matrix (ECM) in species as divergent as cyanobacteria, fly, worm, sea urchin and human. The phyletic distribution of the CSPG repeats suggests that horizontal gene transfer contributed in their evolutionary history. The CSPG domain occurs in 1-15 tandem copies per protein. In some proteins the CSPG repeat is combined with Laminin G domains (see <PDOC50025>) and EGF-like domains [1,2].

The CSPG repeat is likely to obtain an all-β fold, possibly comprising eight β-strands. The sixth β-strand starts with a conserved aromatic residue, which is followed by a conserved serine or threonine. Conserved acidic residues are present in the subsequent loop regions between strands 6 and 7, as well as between 7 and 8. For most β-strands one can observe a typical alternating pattern of hydrophobic and non-hydrophobic residues. Hydrophobic side chains that point to the same side of the β-sheet are probably buried in the interior of the CSPG domain [1].

Some proteins known to contain a CSPG repeat are listed below:

• Mammalian Fras1/Frem family of ECM proteins, associated with epithelial- mesenchymal cohesion during embryonic development.
• Human melanoma-associated chondroitin sulfate proteoglycan (MCSP).
• Rat NG2, the putative rat ortholog of MCSP.

The profile we developed covers the entire CSPG repeat.