Article

A chimeric mechanism for polyvalent trans-phosphorylation of PKA by PDK1

Robert A. Romano 1, Natarajan Kannan 2, Alexandr P. Kornev 3, Craig J. Allison 3, Susan S. Taylor 1 3 4 *

1Departments of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093-0654 2Department of Biochemistry and Molecular Biology and Institute of Bioinformatics, University of Georgia, Athens, Georgia 30602 3Howard Hughes Medical Institute, University of California San Diego, La Jolla, California 92093-0654 4Department of Pharmacology, University of California San Diego, La Jolla, California 92093-0654

email: Susan S. Taylor (staylor@ucsd.edu)

^*Correspondence to Susan S. Taylor, 9500 Gilman Drive, La Jolla, CA 92093-0654

Funded by:
 NIH grant; Grant Number: GM19301

Keywords

PKA • PDK1 • AGC kinases • C-tail • phosphorylation • Ade motif • HF motif • turn motif

Abstract

Phosphorylation on the activation loop of AGC kinases is typically mediated by PDK1. The precise mechanism for this in-trans phosphorylation is unknown; however, docking of a hydrophobic (HF) motif in the C-tail of the substrate kinase onto the N-lobe of PDK1 is likely an essential step. Using a peptide array of PKA to identify other PDK1-interacting sites, we discovered a second AGC-conserved motif in the C-tail that interacts with PDK1. Since this motif [FD(X)1-2Y/F] lies in the active site tether region and in PKA contributes to ATP binding, we call it the Adenosine binding (Ade) motif. The Ade motif is conserved as a PDK1-interacting site in Akt and PRK2, and we predict it will be a PDK1-interacting site for most AGC kinases. In PKA, the HF motif is only recognized when the turn motif Ser338 is phosphorylated, possibly serving as a phosphorylation switch that regulates how the Ade and HF motifs interact with PDK1. These results demonstrate that the extended AGC C-tail serves as a polyvalent element that trans-regulates PDK1 for catalysis. Modeling of the PKA C-tail onto PDK1 structure creates two chimeric sites; the ATP binding pocket, which is completed by the Ade motif, and the C-helix, which is positioned by the HF motif. Together, they demonstrate substrate-assisted catalysis involving two kinases that have co-evolved as symbiotic partners. The highly regulated turn motifs are the most variable part of the AGC C-tail. Elucidating the highly regulated cis and trans functions of the AGC tail is a significant future challenge.

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Received: 18 February 2009; Revised: 6 April 2009; Accepted: 9 April 2009

Digital Object Identifier (DOI)

10.1002/pro.146  About DOI