ZU5-ANK displays a conserved, positively charged surface patch. (A) The electrostatic map (left) of ZU5-ANK subdomain of ankyrin displays a positively charged patch on its surface attributable to the presence of several positively charged amino acids. The basic residues involved are shown in the ribbon diagram (right) shown in the same orientation as the electrostatic surface. Only the side chains of the positively charged residues are shown (ball-and-stick). The middle panel shows the electrostatic map rotated 180° from the left panel and serves to illustrate that only one surface shows the positively charged patch. The molecular surface of the molecule is shown with the equipotential electrostatic surface mapped onto it at ± 15 K_bT/e_c. (B) Sequence alignment of 3 major human ankyrin isoforms (R, B, and G) indicates that many of the charged residues, boxed in blue, are highly conserved at the sequence level and are likely to form part of similar charged surfaces. The secondary structure elements in the structure are shown above the sequence (helices are shown as rectangles, sheets as arrows, and loops as dashed lines). The black box identifies the canonical ZU5 region.⁴⁶