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Cyclin-stimulated binding of Cks proteins to cyclin-dependent kinases
1Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520-8024, USA.
Abstract:
Although Cks proteins were the first identified binding partners of cyclin-dependent protein kinases (cdks), their cell cycle functions have remained unclear. To help elucidate the function of Cks proteins, we examined whether their binding to p34(cdc2) (the mitotic cdk) varies during the cell cycle in Xenopus egg extracts. We observed that binding of human CksHs2 to p34(cdc2) was stimulated by cyclin B. This stimulation was dependent on the activating phosphorylation of p34(cdc2) on Thr-161, which follows cyclin binding and is mediated by the cdk-activating kinase. Neither the inhibitory phosphorylations of p34(cdc2) nor the catalytic activity of p34(cdc2) was required for this stimulation. Stimulated binding of CksHs2 to another cdk, p33(cdk2), required both cyclin A and activating phosphorylation. Our findings support recent models that suggest that Cks proteins target active forms of p34(cdc2) to substrates.
Insights
Cks proteins bind to cyclin-dependent protein kinases (cdks) during the cell cycle. This binding is regulated by specific phosphorylations and cyclins, suggesting Cks proteins target active cdks.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Cks proteins are known binding partners of cyclin-dependent protein kinases (cdks).
- The precise cell cycle functions of Cks proteins remain largely unelucidated.
- Understanding Cks protein function is crucial for comprehending cell cycle regulation.
Purpose of the Study:
- To investigate the cell cycle-dependent binding of Cks proteins to cyclin-dependent protein kinases (cdks).
- To elucidate the regulatory mechanisms governing Cks protein interaction with specific cdks.
- To determine the role of phosphorylation and cyclin binding in Cks-cdk interactions.
Main Methods:
- Utilized Xenopus egg extracts to study protein interactions.
- Examined the binding of human CksHs2 to p34(cdc2) (mitotic cdk) and p33(cdk2).
- Assessed the impact of cyclin B, cyclin A, and phosphorylation states on Cks-cdk binding.
Main Results:
- Human CksHs2 binding to p34(cdc2) was enhanced by cyclin B.
- This stimulation depended on Thr-161 phosphorylation of p34(cdc2), mediated by cdk-activating kinase.
- CksHs2 binding to p33(cdk2) required both cyclin A and activating phosphorylation.
- Inhibitory phosphorylations and catalytic activity of p34(cdc2) were not necessary for stimulated binding.
Conclusions:
- Cks protein binding to cdks is regulated by specific cyclin interactions and activating phosphorylation.
- These findings support models where Cks proteins direct active cdks to their substrates.
- Cks proteins play a role in targeting specific active forms of cdks during the cell cycle.