Originally published as Genetics Published Articles Ahead of Print on April 13, 2009.

Genetics, Vol. 182, 529-539, June 2009, Copyright © 2009
doi:10.1534/genetics.109.102178

Distal Recognition Sites in Substrates Are Required for Efficient Phosphorylation by the cAMP-Dependent Protein Kinase

Stephen J. Deminoff*, Vidhya Ramachandran*,{dagger} and Paul K. Herman*,{dagger},1

* Department of Molecular Genetics, {dagger} Program in Molecular, Cellular and Developmental Biology, The Ohio State University, Columbus, Ohio 43210

1 Corresponding author: Department of Molecular Genetics, Ohio State University, 484 W. 12th Ave., Room 984, Columbus, OH 43210.
E-mail: herman.81{at}osu.edu

Protein kinases are important mediators of signal transduction in eukaryotic cells, and identifying the substrates of these enzymes is essential for a complete understanding of most signaling networks. In this report, novel substrate-binding variants of the cAMP-dependent protein kinase (PKA) were used to identify substrate domains required for efficient phosphorylation in vivo. Most wild-type protein kinases, including PKA, interact only transiently with their substrates. The substrate domains identified were distal to the sites of phosphorylation and were found to interact with a C-terminal region of PKA that was itself removed from the active site. Only a small set of PKA alterations resulted in a stable association with substrates, and the identified residues were clustered together within the hydrophobic core of this enzyme. Interestingly, these residues stretched from the active site of the enzyme to the C-terminal substrate-binding domain identified here. This spatial organization is conserved among the entire eukaryotic protein kinase family, and alteration of these residues in a second, unrelated protein kinase also resulted in a stable association with substrates. In all, this study identified distal sites in PKA substrates that are important for recognition by this enzyme and suggests that the interaction of these domains with PKA might influence specific aspects of substrate binding and/or release.