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Generation and characterization of ATP analog-specific protein kinase Cδ
Varun Kumar1, Yi-Chinn Weng1, Werner J Geldenhuys2
1From the Department of Biological Sciences, School of Biomedical Sciences, Kent State University, Kent, Ohio 44242.
Abstract:
To better study the role of PKCδ in normal function and disease, we developed an ATP analog-specific (AS) PKCδ that is sensitive to specific kinase inhibitors and can be used to identify PKCδ substrates. AS PKCδ showed nearly 200 times higher affinity (Km) and 150 times higher efficiency (kcat/Km) than wild type (WT) PKCδ toward N(6)-(benzyl)-ATP. AS PKCδ was uniquely inhibited by 1-(tert-butyl)-3-(1-naphthyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine (1NA-PP1) and 1-(tert-butyl)-3-(2-methylbenzyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine (2MB-PP1) but not by other 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1) analogs tested, whereas WT PKCδ was insensitive to all PP1 analogs. To understand the mechanisms for specificity and affinity of these analogs, we created in silico WT and AS PKCδ homology models based on the crystal structure of PKCι. N(6)-(Benzyl)-ATP and ATP showed similar positioning within the purine binding pocket of AS PKCδ, whereas N(6)-(benzyl)-ATP was displaced from the pocket of WT PKCδ and was unable to interact with the glycine-rich loop that is required for phosphoryl transfer. The adenine rings of 1NA-PP1 and 2MB-PP1 matched the adenine ring of ATP when docked in AS PKCδ, and this interaction prevented the potential interaction of ATP with Lys-378, Glu-428, Leu-430, and Phe-633 residues. 1NA-PP1 failed to effectively dock within WT PKCδ. Other PP1 analogs failed to interact with either AS PKCδ or WT PKCδ. These results provide a structural basis for the ability of AS PKCδ to efficiently and specifically utilize N(6)-(benzyl)-ATP as a phosphate donor and for its selective inhibition by 1NA-PP1 and 2MB-PP1. Such homology modeling could prove useful in designing molecules to target PKCδ and other kinases to understand their function in cell signaling and to identify unique substrates.
Insights
Researchers engineered an ATP analog-specific PKCδ (AS PKCδ) for studying protein kinase C delta (PKCδ) function and disease. This novel enzyme exhibits enhanced affinity and efficiency, enabling targeted substrate identification and inhibitor development.
Area of Science:
- Biochemistry and Molecular Biology
- Enzyme Engineering
- Structural Biology
Background:
- Protein kinase C delta (PKCδ) plays a crucial role in cellular signaling pathways, and understanding its function in normal physiology and disease states is essential.
- Existing methods for studying PKCδ are limited, necessitating the development of novel tools for precise investigation of its activity and substrate interactions.
Purpose of the Study:
- To develop an ATP analog-specific (AS) PKCδ mutant that allows for targeted substrate identification and selective inhibition.
- To elucidate the structural basis for the enhanced affinity and specificity of AS PKCδ towards ATP analogs and kinase inhibitors.
Main Methods:
- Engineering of an ATP analog-specific PKCδ (AS PKCδ) mutant.
- Biochemical assays to determine substrate affinity (Km) and catalytic efficiency (kcat/Km) of AS PKCδ compared to wild type (WT) PKCδ.
- In silico homology modeling of WT and AS PKCδ based on existing crystal structures to analyze inhibitor and substrate binding.
- Docking studies of ATP analogs and specific inhibitors (1NA-PP1, 2MB-PP1) within the homology models.
Main Results:
- AS PKCδ demonstrated significantly higher affinity (approx. 200-fold) and efficiency (approx. 150-fold) for N(6)-(benzyl)-ATP compared to WT PKCδ.
- AS PKCδ was uniquely inhibited by specific pyrazolopyrimidine (PP1) analogs (1NA-PP1 and 2MB-PP1), while WT PKCδ remained insensitive to all tested PP1 analogs.
- In silico modeling revealed that N(6)-(benzyl)-ATP binds effectively in AS PKCδ but is displaced in WT PKCδ, explaining the specificity. Inhibitor docking explained the selective inhibition of AS PKCδ.
Conclusions:
- The developed AS PKCδ provides a powerful tool for studying PKCδ function, identifying its substrates, and developing targeted inhibitors.
- The structural insights gained from homology modeling offer a foundation for designing novel kinase inhibitors with improved specificity.
- This engineered kinase system has broad implications for understanding kinase signaling in health and disease.
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