Document Type


Publication Date

August 2007


This article has been peer reviewed. It is the authors' final version prior to publication in Structure 15(12):1591-1602, December 2007. The published version is available at Copyright © 2007 by Elsevier, Inc.


Phosphorylation of endogenous inhibitor proteins specific for type-1 Ser/Thr phosphatase (PP1) provides a mechanism for reciprocal coordination of kinase and phosphatase activities. Phosphorylation of Thr38 in the inhibitor protein CPI-17 transduces G-protein-mediated signaling into a > 1000-fold increase of inhibitory potency toward myosin phosphatase. We show here the solution NMR structure of phospho-T38-CPI-17 with r. m. s. d. of 0.36 ± 0.06 Å for the backbone secondary structure, which reveals how phosphorylation triggers a conformational change and exposes the PP1 inhibitory surface. This active conformation is stabilized by the formation of a hydrophobic core of intercalated side-chains, which is not formed in a phospho-mimetic D38 mutant form of CPI-17. Thus, the profound increase in potency of CPI-17 arises from phosphorylation, conformational change and hydrophobic stabilization of a rigid structure that poses the phosphorylated residue on the protein surface and restricts its hydrolysis by myosin phosphatase. Our results provide structural insights into transduction of kinase signals by PP1 inhibitor proteins.

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