Figure 3.

Structural basis for reaction order. (A) Model of MAP2K activation loop (yellow) docking in the MAP3K (gray) based on peptide docking on protein kinase A (PDB:1ATP). (Blue) A positively charged patch that interacts with the exposed aspartic acid; (brown) a hydrophobic patch that interacts with the isoleucine. (B) Cartoon representation of peptide docking models for MAP3Ks and MAP2Ks. (Blue regions) Areas of positive surface charge; (brown areas) exposed hydrophobic regions. (Red spheres) Phosphorylation sites. (Orange) Activation loop of the MAP3K; (yellow) activation loop of the MAP2K; (purple) activation loop of the MAPK. The MAP2K cartoon represents the structure and interactions during the first step of MAPK phosphorylation (on Tyr). (White lines) Predicted hydrogen bonds between the activation loops. To see this figure in color, go online.