Structure of SPTAN1. SPTAN1 harbors 22 domains, which are presented in green. Shown are the following: characteristic spectrin repeats (green boxes); C- and N-terminus (green rectangle); domain 10 with a SH3 domain (blue circle), which allows binding of EVL, TES, and FANCG; a 20 amino acid (aa) motif and alternatively spliced region between domains 10 and 11, which allows specific binding of Connexin 43 (Cox43); phosphorylation site (orange) at residue Y1176 in domain 11 and behind that the calpain cleavage site of SPTAN1 and the calmodulin (CaM) binding site, which regulates calpain-mediated proteolysis; a potential MLH1 binding site between domains 18 and 22; potential cystein (C) residues (orange lines) in domain 20, which might mediate a potential E2/E3 ubiquitin-protein-conjugating or -ligating activity; domains 20 and 21, which mediate dimerization of SPTAN1 and SPTBN1 by binding to the N-terminal first two spectrin repeats of SPTBN1 (yellow)  and C-terminal the CaM-like domain 22, which can bind calcium through two EF-hand motifs. Translational inhibition by miRNA-128-3p targets the 3′ untranslated region (3′UTR) of SPTAN1 . SPTBN1 can bind actin through its N-terminal Calponin homology (CH) domain . Spectrin heterodimers formed by antiparallel lateral dimerization of SPTAN1 and SPTBN1 then form tetramers by head to head assembly [3, 4]. Modified after Bennett and Baines (2001) and Baines (2010) [4, 17].