_-Spectrin (FDRN) was first described in the erythrocyte in which it
reinforces the cell membrane by cross linking ankyrin and protein
4.1. Nonerythroid _II-spectrin and its close homolog, _-fodrin, form
elongated double stranded filaments. Each strand consists of segments
of triple stranded _-helices that are formed by the strand going
forward, back, forward. The two EF-hands at the C-terminus impart a
calcium sensitive  interaction with actin and other cytosolic
proteins . The first domains of ACTN and FDRN are most closely
related; their second EF-hands are also quite similar to one another.
Portions of the non-EF-hand regions of ACTN and FDRN appear to be
related; the two are placed in distinct subfamilies because of their
different interactions with the cytoskeleton.