Figure 3.

Structure of the inhibitor peptide PKI bound to the PKA enzyme: N-terminal region of the substrate. Key arginines from the substrate peptide (RCSB Protein Data Bank entry 1JLU [92]) are highlighted. The left part of the figure shows the surface of PKA in ochre, the backbone of the substrate peptide in silver and the arginines -6, -3 and -2 of the substrate in blue. Arginines -3 and -2 interact with the binding cleft and thereby make major contributions to substrate specificity. A set of acidic enzyme residues interacts with these arginines (zoomed detail-view to the right): Glu170 and Glu230 for Arg-2, Glu127 for Arg-3 and Glu203 for Arg-6 [3]. The pictures were generated using VMD [93].