Protein Kinase A: Difference between revisions

PKA consists of two types of subunits. It has a 49-kd regulatory <scene name='58/582909/Rs/1'>regulatory subunit</scene> (R) and a 38-kd <scene name='58/582909/Cs/1'>catalytic subunit</scene> (C). The R dimer contains two cAMP bindng domains and the pseudosubstrate sequence, Arg-Arg-Gly-Ala-Ile. The C subunit has two lobes. The larger lobe binds the peptide and contributes the key catalytic residues and the smaller lobe binds ATP-Mg2+. This <scene name='58/582909/Catalytic_subunit_1/1'>scene</scene> shows a catalytic subunit with an inhibitor with a  <scene name='58/582909/Psuedosubstrate/1'>pseudosubstrate</scene> bound to the active site and an ATP bound to the adjacent active site. When PKA is enzymatically inactive (absence of cAMP), it is a heterotetrameric complex of a regulatory dimer bound to two catalytic subunits, forming the R2C2 complex. In its active state, the complex dissociates to form an R2 subunit and two C subunits. The C subunits are enzymatically active in itself and once released, are free to bind and phosphorylate available substrate proteins.