The structural plasticity of the C terminus of p21Cip1 is a determinant for target protein recognition

Area of Science:

• Molecular Biology
• Protein Structure and Dynamics
• Cell Cycle Regulation

Background:

• The cyclin-dependent kinase inhibitory protein p21(Cip1) is crucial for cell-cycle regulation.
• p21(Cip1) interacts with various cellular proteins, including proliferating cell nuclear antigen (PCNA), calmodulin (CaM), and the oncoprotein SET, via its C-terminal domain.
• The structural basis for p21(Cip1) interactions with CaM and SET is poorly understood due to limited structural data.

Purpose of the Study:

• To investigate the molecular mechanism by which the C-terminal domain of p21(Cip1) recognizes multiple ligands.
• To elucidate how the C-terminal domain of p21(Cip1) adopts different conformations upon binding to distinct proteins.

Main Methods:

• Utilized a peptide derived from the C-terminal domain of p21(Cip1) that encompasses the binding sites for PCNA, CaM, and SET.
• Employed biophysical techniques to analyze the conformational changes of the peptide upon ligand binding (details not specified in abstract).

Main Results:

• Demonstrated that the C-terminal domain of p21(Cip1) recognizes multiple ligands by adopting distinct conformations.
• Showed that the specific conformation adopted is determined by tertiary contacts within the protein, not solely the primary sequence.
• Observed that the C-terminal domain adopts an extended structure when bound to PCNA and likely SET, but an alpha-helical structure when bound to CaM.

Conclusions:

• The C-terminal domain of p21(Cip1) exhibits significant conformational flexibility, enabling it to bind diverse proteins.
• Tertiary contacts play a critical role in dictating the specific conformation and thus the ligand specificity of the p21(Cip1) C-terminus.
• This conformational plasticity is key to the multifaceted roles of p21(Cip1) in cellular processes.