Subdomain IX of Kinase Domain of Protein Kinase A

Subdomain IX has the secondary structure of a large alpha helix. Its has a role of structure and of substrate recognition. It contains a invariant Asp residue at postion 220 that acts to stabilize the catalytic loop (present in subdomain VIA) by hydrogen bonding to the the backbone amides of Arg165 and Tyr164, which are present just a few positions preceding the beginning of the catalytic loop. Glu230 in subdomain IX of PKA, which is not an invariant residue, is important in the recogintion of the inhibitor peptide. It does this by forming an ion pair with the second Arg in the recognition consensus. Residues 235-239, Tyr-Pro-Pro-Phe-Phe are all involved in hydrophobic interactions with the pseudosubstrate inhibitor.