Defining the substrate specificity of cdk4 kinase-cyclin D1 complex
R H Grafstrom1, W Pan, R H Hoess
1Genetics and Cancer Group, Dupont Pharmaceutical Co., Wilmington, DE 19880-0336, USA. robert.h.grafstrom@dupontpharma.com
Carcinogenesis
|March 9, 1999
Summary
The cyclin-dependent kinase 4 (CDK4) / cyclin D1 complex preferentially phosphorylates retinoblastoma protein (Rb) at Ser795. Specific amino acid sequences and structural context dictate this phosphorylation site preference.
Area of Science:
- Molecular Biology
- Cell Cycle Regulation
- Protein Phosphorylation
Background:
- The cyclin-dependent kinase 4 (CDK4) / cyclin D1 complex is a key regulator of cell cycle progression.
- Retinoblastoma protein (Rb) is a critical tumor suppressor that controls cell cycle entry.
- Rb is regulated by phosphorylation, with specific sites influencing its function.
Purpose of the Study:
- To identify the preferred phosphorylation site of the CDK4/cyclin D1 complex on Rb.
- To determine the sequence and structural determinants of this phosphorylation specificity.
- To investigate the functional conservation of phosphorylation sites in related proteins.
Main Methods:
- Site-directed mutagenesis of Rb phosphorylation sites.
- In vitro kinase assays using CDK4/cyclin D1 complex.
- Comparison of phosphorylation rates at different Rb and p107 sites.
Main Results:
- Serine 795 (Ser795) in the Rb C-terminal domain is the preferred phosphorylation site for CDK4/D1.
- Arginine at the third position C-terminal to the target serine is crucial for efficient phosphorylation.
- Mutating less favorable sites in Rb to mimic Ser795 enhances CDK4/D1 phosphorylation.
- The Rb Ser795 site can substitute for the p107 Ser842 site without altering phosphorylation rates.
Conclusions:
- Phosphorylation site specificity by CDK4/D1 is determined by both surrounding amino acid sequences and the structural context of the site.
- Understanding these determinants allows for the engineering of specific phosphorylation sites.
- Conserved phosphorylation mechanisms exist between Rb and related proteins like p107.
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