InterPro domain: IPR001298

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 IPR001715 ), their rods fall into three families.

The rod domain of the family including the Dictyostelium discoideum (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 [ 1 ]. 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 [ 2 , 2 ]. 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.

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 [ 3 , 4 , 4 ].

1. The repeating segments of the F-actin cross-linking gelation factor (ABP-120) have an immunoglobulin-like fold. Nat. Struct. Biol. 4, 223-30
2. Structural basis for dimerization of the Dictyostelium gelation factor (ABP120) rod. Nat. Struct. Biol. 6, 836-41
3. Crystallization and preliminary X-Ray diffraction characterization of a dimerizing fragment of the rod domain of the Dictyostelium gelation factor (ABP-120). J. Struct. Biol. 120, 192-5
4. The Dictyostelium gelation factor shares a putative actin binding site with alpha-actinins and dystrophin and also has a rod domain containing six 100-residue motifs that appear to have a cross-beta conformation. J. Cell Biol. 109, 607-18