Protein kinase A

Protein Kinase A (PKA) is a protein that is dependent on cyclic AMP (cAMP) and without it, is deactivated. PKA is involved in signal-transduction pathways and phosphorylates proteins by adding a phosphate group. The molecule consists of two subunits, a regulatory subunit and a calalytic subunit . These subunits are inactive when cAMP is not bound. When cAMP binds to a regulatory subunit a conformational change occurs. This change means that the catalytic subunit becomes active and is no longer inhibited. This means that the protein can now phosphorylate other proteins by removing a phosphate from ATP, and adding it to a serine residue on the target protein which in turn leads to a cellular response .

Protein Kinase A (PKA) is one of the member of family of enyzmes which is functionally dependent on the levels of cyclic-adenomonophopshate (cAMP). It is also commonly known as the cAMP dependent A kinase, therefore it works through the cAMP signalling pathway. Essentially, PKA is responsible for all the cellular responses induced by cAMP second messenger system.

Structure:

PKA is a heterotetramer consists of 4 subunits, of which composed of 2 regulatory and 2 catalytic subunits.

• Regulatory subunit: Two of these subunits are joined together covalently via disulfide bonds. Each subunit has 2 cAMP binding sites, a domain that interacts with the catalytic subunit and a "auto-inhibitory" domain that act as a pseudo-substrate motif RRGA1 for the catalytic subunit.

Two major forms of regulatory subunits exist, RI and RII, each form has two subtypes alpha and beta. Type 1 inhibit different isotypes are encoded by different genes.

• Catalytic subunit: This subunit contains the ATP binding domain and the enzyme's active site. Each subunit is bound to the either side of the regulatory subunit.