Functional studies on the PKA regulatory subunit mutant R74C found in Carney complex (913.11)

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The protein kinase A regulatory type I alpha subunit (PKA RegI) is the cAMP dependent subunit of the PKA holoenzyme. The gene for PKA RegI is located on chromosome 17q23‐17q24 and extends roughly 21 kb in length. PKA RegI is a component of the PKA holoenzyme, which is composed of a dimer of two regulatory subunits bound to a dimer of catalytic subunits (PKA Cat) to create a tetrameric protein in the inactive state. The PKA holoenzyme is activated by each PKA RegI monomer binding two molecules of cAMP at two distinct sites (3). This binding changes the shape of the regulatory subunit, therefore altering its affinity for the catalytic subunit by roughly 4 orders of magnitude (3). This causes the regulatory subunits to dissociate from the catalytic subunits, thereby releasing the catalytic subunits as active monomers to phosphorylate their intracellular targets. In their active state, the catalytic subunits act as active serine‐threonine kinases and have the potential to phosphorylate various targets which may alter muscle contractility as well as cell growth, proliferation and differentiation. PKA RegI is therefore an important protein with a vital role in the cardiovascular system, and its role in other tissues and disease states is being investigated. In particular, the Arg74Cys mutation of PKA RegI is found in Carney Complex, an autosomal dominant disorder that can cause a range of effects including skin lesions, tissue tumors (especially cardiac) and various types of endocrine tumors (1). It is therefore of interest to characterize the functional impact of this missense mutation on PKA RegI function in order to better understand the role of this mutation in the etiology of Carney Complex. Therefore, this study used biochemical and spectroscopic methods to examine the potential impact of the Arg74Cys mutation on the affinity of PKA RegI for both cAMP and its PKA Cat binding partner (2), as well as the effect of this mutation on PKA RegI phosphorylation at a novel downstream serine residue, Ser77.