Modular organization of actin crosslinking proteins.

A family of actin-crosslinking proteins share a conserved 125 residue sequence that lies within a 250 residue actin-binding domain. This domain is combined with spacer segments consisting of a variable number of repeated alpha-helical or beta-sheet motifs and other functional domains, which generate proteins that differ in their ability to form actin bundles or networks and to associate with the plasma membrane. These functional domains are not in other actin-crosslinking proteins, one of which is elongation factor 1a (EF-1a) suggesting there are several pathways for the evolution of actin-crosslinking function.