[Frontiers in Bioscience 7, d580-592, March 1, 2002]


Sharron H. Francis, Celeste Poteet-Smith, Jennifer L. Busch, Robyn Richie-Jannetta, and Jackie D. Corbin

Dept. of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232-0615


1. Abstract
2. Introduction
3. General mechanisms of autoinhibition of cyclic nucleotide-dependent protein kinases
3.1. Autoinhibition through substrate-like sequences
3.2. Autoinhibition through non-substrate like sequences
4. Autoinhibition of cyclic AMP-dependent protein kinases (PKA)
4.1. Studies of autoinhibition of PKA using modified forms of R subunits
4.2. Studies of autoinhibition of PKA using synthetic peptides
4.3. Inhibition of PKA by the heat stable PKA inhibitor, PKI
5. Autoinhibition of cGMP-dependent protein kinases (PKG)
5.1. Studies of PKG autoinhibition using modified PKGs
5.2. Effect of autophosphorylation on PKG autoinhibition
5.3. Inhibition of PKG by RI subunit
5.4. Studies of PKG autoinhibition using synthetic peptides
6. Summary
7. Acknowledgement
8. References


Cyclic AMP-dependent protein kinase (PKA) and cGMP-dependent protein kinase (PKG) are autoinhibited through multiple interactions between their respective regulatory and catalytic domains. A large portion of this autoinhibition occurs through interactions between residues within the catalytic domain and those within either a substrate-like sequence (-RRXSX-) or pseudosubstrate sequence (-RRXAX-) in the regulatory domains. These contacts effectively inhibit catalysis by blocking substrate binding. Particularly important contacts involve the P-2, P-3, and P+1 residues where either serine, which is potentially autophosphorylated, or alanine occupies the P0 position. The primary sequence is apparently less important for autoinhibition in PKGs than in PKAs, and a conserved serine at P+2 in PKGs is important for autoinhibitory contacts. Elements outside the substrate-related sequences also contribute to autoinhibition in both PKA and PKG. For example, synthetic peptides with relatively short pseudosubstrate sequences are weak inhibitors; while heat-denatured RII subunit does not inhibit catalytic subunit, it is still rapidly autophosphorylated; and truncated PKGs lacking the substrate-like sequence are still partially autoinhibited. Thus, capacity for autoinhibition of PKA or PKG is provided by contacts involving direct interactions with the catalytic site and by contacts that stabilize an inactive conformation.