dimerization/docking (D/D) domain of the Type II beta Regulatory subunit of cAMP-dependent protein kinase
cAMP-dependent protein kinase (PKA) is a serine/threonine kinase (STK), catalyzing the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. The inactive PKA holoenzyme is a heterotetramer composed of two phosphorylated and active catalytic subunits with a dimer of regulatory (R) subunits. Activation is achieved through the binding of the important second messenger cAMP to the R subunits, which leads to the dissociation of PKA into the R dimer and two active subunits. There are two classes of R subunits, RI and RII; each exists as two isoforms (alpha and beta) from distinct genes. These functionally non-redundant R isoforms allow for specificity in PKA signaling. RII subunits contain a phosphorylation site in their inhibitory site and are both substrates and inhibitors. RIIbeta plays an important role in adipocytes and neuronal tissues. Mice deficient with RIIbeta have small fat cells, and are resistant to obesity, diet-induced diabetes, and alcohol-induced motor defects. The R subunit contains an N-terminal dimerization/docking (D/D) domain, a linker with an inhibitory sequence, and two c-AMP binding domains. The D/D domain dimerizes to form a four-helix bundle that serves as a docking site for A-kinase-anchoring proteins (AKAPs), which facilitates the localization of PKA to specific sites in the cell. PKA is present ubiquitously in cells and interacts with many different downstream targets. It plays a role in the regulation of diverse processes such as growth, development, memory, metabolism, gene expression, immunity, and lipolysis.
Jiyao W et al.(2023). "The conserved domain database in 2023.",