Comparison of the structures of phosphopeptides bound to Grb2 SH2.

(A) CD28 (present work, D-pY-M-N-M-T). (B) BCR-Abl (a typical type-I β-turn, PDB ID: 1BMB, F-pY-V-N-V-E) (C) AICD (with a Pro residue at the pY+3 position, PDB ID: 3MXC, G-pY-E-N-P-T-Y). The SH2 domains are shown as surface models, whereas the phosphopeptides are shown as stick models. The thin green lines indicate the distance between the main-chain O of pY and the main-chain N of pY+3, which form a hydrogen bond in the type-I β-turn. The side-chains of some flanking residues are missing due to their weak electron density. (D) Superposition of the 3 peptides. The tubes represent the main-chain traces of CD28 (green), BCR-Abl (red), and AICD (blue). (E) Superposition of CD28, BCR-Abl, and AICD as in (D) but vertically rotated by approximately 90°.