Figure 2.

The eukaryotic PK in the AGC group and its PSDRs. (a) The two-lobe structure of PKA (22) with PSDRs shown by space-fill. The two lobes are red and blue, respectively. The inhibitor substrate (yellow) lies between the lobes. Phospho-Thr-197 is green. (b) PSDRs are as follows: Lys-83, Gln-84, His-87 (blue, upper) Ser 53 (blue, lower) of the PKA and His-23 (yellow) of the inhibitor. Ala-21 (magenta) is the P site. His-23 is the P + 2 site. (c) Phe-129 and Arg-133 (blue) of the PKA, and Arg-18 and Arg-19 on the inhibitor (yellow). The P site is magenta. Arg-18 and Arg-19 correspond to P− 3 and P − 2, respectively. (d) PSDRs Val-191 (red, upper), Tyr-196 (red), Lys-83, and His-87 (blue). Phospho-Thr-197 is green. His-23 and Asp-24 (yellow) are the closest substrate residues to Tyr-196, but are clearly not in contact with Tyr-196.