The crystal structure of the ankyrin-binding domain of erythroid spectrin. (A) Ribbon diagram of the βI-14,15 di-repeat. The 14th repeat (βI-14) is shown in blue, the 14,15 linker is shown in gold, and the 15th repeat (βI-15) is red. The dashed line designates the disordered 15A-B loop. Other secondary structure elements are labeled as in the text. (B) Experimental SAD-phased electron-density map covering the 14th repeat of βI spectrin (blue mesh) calculated to 2.5 Å and contoured at 1.5σ. The Cα trace of the final model of βI-14,15 (orange) is superimposed.