Filamins: promiscuous organizers of the cytoskeleton

Filamins are elongated homodimeric proteins that crosslink F-actin. Each monomer chain of filamin comprises an actin-binding domain, and a rod segment consisting of six (Dictyostelium filamin) up to 24 (human filamin) highly homologous repeats of approximately 96 amino acid residues, which adopt an immunoglobulin-like fold. Two hinges in the rod segment, together with the reversible unfolding of single repeats, might be the structural basis for the intrinsic flexibility of the actin networks generated by filamins. There are numerous filamin-binding proteins that associate, in most cases, along the repeats of the rod repeats. This rather promiscuous behaviour renders filamin a versatile scaffold between the actin network and finely tuned molecular cascades from the membrane to the cytoskeleton.