The structure of the ZU5 domain of ankyrin helps understand general features of this domain. (A) The ribbon diagram shows the ankyrin ZU5 domain (ZU5-ANK). The region corresponding to the canonical ZU5 region is shown in blue, whereas the last 55 amino acids forming this domain are shown in red. The diagram illustrates that 2 of the β strands in the β-sheet core come from residues lying outside the ZU5 consensus region, suggesting that the ZU5 consensus may extend beyond the canonical boundaries. (B) The ribbon diagram shows the functional mutants of ankyrin that map to the ZU5-ANK structure. The mutants are mostly found on the surface of a single face of the molecule. One of the mutations was mapped from an ankyrin variant implicated in hereditary spherocytosis and corresponds to L1046P,⁴⁸  whereas other are functional mutants (DAR920AAA, A945P, ESY1026AAA, EE1044AA, KR1049AA) mapped from mutagenesis studies in other ankyrin isoforms that impair spectrin-binding activity in cell culture.⁴⁹  Only the side chains of these mutants are shown (ball-and-stick). (C) Sequence alignment of human ankyrin R and 4 other ZU5 domain-containing proteins: Caenorhabditis elegans UNC-44, human netrin receptor, C elegans UNC-5, and human zona occludens-1. In correspondence with the color coding in panel A, the ZU5 domain⁴⁶  is boxed blue whereas approximately 50 residues C-terminal to each protein's ZU5 consensus region (when available) are boxed in orange. Secondary structure assignments based on the structure of ZU5-ANK are provided above the sequence alignment as in Figure 3B. Residues printed in red indicate the locations of the functional mutants depicted in panel B. Individually boxed residues denote sites of universal (blue) or high (green) conservation among the presented sequences.