Filamin/ABP280 repeat <p>The many different actin cross-linking proteins share a common architecture, consisting of a globular actin-binding domain and an extended rod. Whereas their actin-binding domains consist of two calponin homology domains (see <db_xref db="INTERPRO" dbkey="IPR001715"/>), their rods fall into three families.</p><p>The rod domain of the family including the <taxon tax_id="44689">Dictyostelium discoideum</taxon> (Slime mould) gelation factor (ABP120) and human filamin (ABP280) is constructed from tandem repeats of a 100-residue motif that is glycine and proline rich [<cite idref="PUB00003939"/>]. The gelation factor's rod contains 6 copies of the repeat, whereas filamin has a rod constructed from 24 repeats. The resolution of the 3D structure of rod repeats from the gelation factor has shown that they consist of a beta-sandwich, formed by two beta-sheets arranged in an immunoglobulin-like fold [<cite idref="PUB00003939"/>, <cite idref="PUB00010567"/>]. Because conserved residues that form the core of the repeats are preserved in filamin, the repeat structure should be common to the members of the gelation factor/filamin family.</p><p>The head to tail homodimerisation is crucial to the function of the ABP120 and ABP280 proteins. This interaction involves a small portion at the distal end of the rod domains. For the gelation factor it has been shown that the carboxy-terminal repeat 6 dimerises through a double edge-to-edge extension of the beta-sheet and that repeat 5 contributes to dimerisation to some extent [<cite idref="PUB00010566"/>, <cite idref="PUB00010567"/>, <cite idref="PUB00010568"/>].</p>