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Solution structure of p21(Waf1/Cip1/Sdi1) C-terminal domain bound to Cdk4
1Department of Biochemistry and Protein-Network Research Center, College of Science, Yonsei University, Seoul, 120-749, Korea.
Abstract:
Cyclin-dependent kinase (Cdk) inhibitor p21(Waf1/Cip1/Sdi1), a multifunctional protein, has a major role as tumor suppressor, mediating G1/S arrest through inhibition of Cdks. Recent biological studies of Cyclin D1/Cdk4 have proposed that p21 C-terminal domain (p21(CT)) plays a key role as a potent Cdk4 inhibitor. We report here solution structures of p21(CT) for both the free and Cdk4-bound forms using 2D transferred NOE spectroscopy and dynamical simulated annealing calculations. Even though p21(CT) peptide is very flexible in the free state, when it bound to Cdk4, the structure becomes well structured in the binding domain. Therefore we propose that p21(CT) experiences an extensive conformational change upon Cdk4 binding. This structural change of p21(CT) may suggest the molecular mechanism of p21 for specificity and inhibition mode to assemble different cyclin-Cdk complexes. Especially, our data suggests that the D(149)FYHSKRR(156) region of p21 is critical for Cdk4 binding, indicating that the major driving force for complex originates from hydrophobic interaction between p21 and Cdk4.
Insights
The p21 C-terminal domain (p21(CT)) acts as a potent Cdk4 inhibitor. Upon binding Cdk4, p21(CT) undergoes a conformational change, revealing a critical binding region essential for complex formation.
Area of Science:
- Molecular Biology
- Structural Biology
- Biochemistry
Background:
- p21(Waf1/Cip1/Sdi1) is a multifunctional protein acting as a tumor suppressor by inhibiting cyclin-dependent kinases (Cdks).
- Recent studies suggest the C-terminal domain of p21 (p21(CT)) is crucial for inhibiting the Cyclin D1/Cdk4 complex.
Purpose of the Study:
- To determine the solution structures of the p21 C-terminal domain (p21(CT)) in its free and Cdk4-bound states.
- To elucidate the structural basis for p21's inhibition and specificity towards Cdk4.
Main Methods:
- 2D transferred NOE spectroscopy was employed to study the protein structures.
- Dynamical simulated annealing calculations were used to refine the structural models.
Main Results:
- The p21(CT) peptide is flexible in its free state but becomes well-structured upon binding to Cdk4.
- A significant conformational change in p21(CT) occurs upon Cdk4 complexation.
- The D(149)FYHSKRR(156) region of p21 was identified as critical for Cdk4 binding.
- Hydrophobic interactions are indicated as the primary driving force for p21-Cdk4 complex formation.
Conclusions:
- p21(CT) undergoes an extensive conformational change upon binding Cdk4, contributing to its inhibitory function.
- This structural plasticity may explain the specificity and inhibition mechanisms of p21 with different cyclin-Cdk complexes.
- The identified binding region and hydrophobic interactions provide insights into the molecular mechanism of p21-Cdk4 inhibition.