Structure of the human β I-spectrin/ZU5-ankyrin R complex. (A) HEβ −1315 (blue) comprises 3 tandem canonical spectrin repeats (teal, blue, and dark blue from N- to C-terminus), each folded into a 3-helix bundle with the repeats connected by α-helical linkers. ZU5-ANK (gold), the spectrin binding domain of ankyrin R, maintains a compact β-sandwich fold connected by extended loops. The main interacting surfaces of the complex are formed by helices A and C of repeat 14 and the B/C loop of repeat 15 in β-spectrin and by the 2 strands from the β-core as well as 2 loops of ZU5-ANK. The 2 views are related by a 90° rotation. (B) Three different views of the spectrin/ankyrin interaction, that is, along the C-terminus of helix C of repeat 14 of spectrin (top), near the B/C loop of repeat 15 (middle), and near the N-terminus of helix C of repeat 14 (bottom).