Protein , association regulatory subunits

An increase in cAMP and activation of protein kinase A are accompanied, in many cases, by a change in the subcellular location of the protein kinase A holoenzyme and the catalytic subunit. In particular, protein kinase A in cells of the nerve system is often found associated with the cytoskeleton. This association is mediated by the RII subunit. Binding of cAMP to the regulatory subunit releases the catalytic subunit that can phosphorylate substrates in the near vicinity. The released catalytic subunit can also be transferred to other compartments of the cell. Parallel to the increase in cAMP, translocation of the catalytic subunit is observed in many cells from the Golgi apparatus to the nucleus via the cytosol, and is accompanied by stimulation of transcription. 

Another second-messenger-dependent kinase which interacts with targeting proteins, is the cAMP-dependent protein kinase A. PKA interacts with AKAPs (A-kinase-associated proteins). AKAPs bind to the dimeric form of the regulatory subunit of PKA. They are multivalent linkers, which bind not only to PKA, but also to other kinases, such as PKC, and the Ca +Z calmodulin-dependent kinase II and the phosphatase PP2B (Fig. 7.6). 

Zolnierowicz S, Van Hoof C, Andjelkovic N et al (1996) The variable subunit associated with protein phosphatase 2Ao defines a novel multimember fiimily of regulatory subunits. Biochem J 317 187-194... 

Some ligand-activated membrane receptors transmit their signal by stimulating adenylate cyclase activity in the cell to produce cAMP. This activation pathway is mediated by a receptor-associated G protein called GS (Chapter 16). In mammals, the most common mechanism by which cAMP serves as a second messenger involves cAMP binding to the regulatory subunit of cAMP-dependent protein kinase A (PKA). Dissociation of the regulatory subunit allows the catalytic sub-... 

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