α-actinin is a F-actin cross-linking protein which is thought to anchor actin to a variety of intracellular structures [1]. The actin-binding domain of α-actinin seems to reside in the first 250 residues of the protein. A similar actin-binding domain has been found in the N-terminal region of many different actin-binding proteins [2,3]:

• In the β chain of spectrin (or fodrin).
• In dystrophin, the protein defective in Duchenne muscular dystrophy (DMD) and which may play a role in anchoring the cytoskeleton to the plasma membrane.
• In the slime mold gelation factor (or ABP-120).
• In actin-binding protein ABP-280 (or filamin), a protein that link actin filaments to membrane glycoproteins.
• In fimbrin (or plastin), an actin-bundling protein. Fimbrin differs from the above proteins in that it contains two tandem copies of the actin- binding domain and that these copies are located in the C-terminal part of the protein.

We selected two conserved regions as signature patterns for this type of domain. The first of this region is located at the beginning of the domain, while the second one is located in the central section and has been shown to be essential for the binding of actin.