Residues critical for ankyrin binding are located around and within the 14,15 linker. In the center panel, the molecular surface and the coil representation of the βI spectrin di-repeat structure are shown. Solvent-exposed residues critical for ankyrin recognition are red; buried residues are green; the remaining residues are colored light blue. The view in the left panel is the same as in Figure 2A, whereas the right panel view is rotated ∼90° clockwise around the vertical axis. (A) Detailed view of the putative ankyrin-recognition surface with the critical residues represented as red ball-and-stick. (B) Interactions in the hydrophobic core of βI-14 with the important hydrophobic residues in green and other interacting residues shown as beige ball-and-stick. (C) The role of Y₁₈₀₂ in stabilizing the structure of βI-15. The side-chain of Y₁₈₀₂ (green) forms interactions with residues from all 3 helices of the 15th repeat (beige). (D) Interactions in the 14,15 linker region. The side-chains of S₁₇₉₆ and Y₁₈₆₆ (green) interact with residues from both repeats (beige) and appear to be critical for determining the relative orientation of the two repeats. The water molecule is shown as red sphere, while the dashed lines indicate hydrogen bonds. The major secondary structure elements are labeled in italic.