Fig. 2. Structures of ectodomain fragments of both NOTCH1 and JAGGED1, and models for the Notch ectodomain. (A) NMR structure of EGF-like repeats 11-13 from human NOTCH1 (PDB ID code 1TOZ). Two of the 20 calculated structures in the ensemble are shown: the double-headed arrow indicates the range of positions that are occupied by repeat 13 among the 20 calculated structures. Disulfide bonds are colored orange; hydrophobic residues engaged in interdomain contacts are shown as sticks. Bound Ca²⁺ ions, positioned on the basis of structural alignment with other Ca²⁺-binding EGF-like repeats, are shown as green spheres. (B,C) Two proposed models for the overall organization of a Notch ectodomain. In B, a rod-like, extended model is shown, whereas C illustrates one possible compact model. EGF-like repeats (ovals) are shaded dark purple when they contain a consensus Ca²⁺-binding site (per the definition used by UniProt) and light purple when they do not. (D) Representation of the X-ray structure for the JAGGED1 polypeptide (PDB code 2VJ2), comprising the DSL domain and EGF-like repeats 1-3. Disulfide bonds are yellow. Side-chains of residues at the proposed Notch-binding surface are rendered as colored sticks.