Design, Heterologous Expression, and Application of an Immobilized Protein Kinase

Protein kinase A (PKA) is a biologically important enzyme for cell regulation, often referred to as the "central kinase". An immobilized PKA that retains substrate specificity and activity would be a useful tool for laboratory scientists, enabling targeted phosphorylation without interference from downstream kinase contamination or kinase autophosphorylation in sensitive assays. Moreover, it might also provide the benefits of robustness and reusability that are often associated with immobilized enzyme preparations. In this work, we describe the creation of a recombinant PKA fusion protein that incorporates the HaloTag covalent immobilization system. We demonstrate that protein fusion design, including affinity tag placement, is critical for optimal heterologous expression in Escherichia coli. Furthermore, we demonstrate various applications of our immobilized PKA, including the phosphorylation of recombinant PKA substrates, such as vasodilator-stimulated phosphoprotein, and endogenous PKA substrates in a cell lysate. This immobilized PKA also possesses robust activity and reusability over multiple trials. This work holds promise as a generalizable strategy for the production and application of immobilized protein kinases.