Model of the dystrophin molecule

Dystrophin, the largest member of the spectrin
superfamily, is composed of 3685 amino acids
(molecular mass 427 kDa) which form four
functional domains: (1) the N-terminal actinbinding
domain of 336 amino acids; (2) 24 long
repeating units, each consisting of 88- to 126-
amino-acid triple-helix segments as in spectrin;
(3) a 135-amino-acid cysteine-rich
domain, which binds to the sarcolemma proteins;
and (4) the C-terminal domain of 320
amino acids with binding sites to syntrophin
and dystrobevin. The triple helix segments form
the central rod domain, which is 100–125 nm
long.