Extreme multivalency and a composite short linear motif facilitate PCNA-binding, localisation and abundance of p21...

Area of Science:

• Molecular biology
• Biophysics
• Cell biology

Background:

• Cyclin-dependent kinase inhibitor 1 (CDKN1A; p21) is crucial for cell cycle arrest, DNA replication, and repair.
• p21 interacts with proliferating cell nuclear antigen (PCNA) via a C-terminal short linear motif (SLiM) for high-affinity binding.
• The molecular mechanisms of PCNA-p21 interaction and the role of flanking regions in p21 functions remain largely unknown.

Purpose of the Study:

• To investigate the molecular details of the interaction between PCNA and p21 flanking regions.
• To determine the role of flanking regions' charge composition in PCNA binding and other p21 functions.
• To explore the implications of composite SLiMs for understanding protein function and drug development.

Main Methods:

• Biophysical techniques were employed to study the interaction between PCNA and various p21 variants.
• p21 variants with altered Lys/Arg compositions and D-amino acids in flanking regions were utilized.
• Cell-based experiments assessed p21 abundance and nuclear localization.

Main Results:

• PCNA-p21 flanking region interaction is driven by charge complementarity rather than specific contacts.
• The precise Lys/Arg composition of flanking regions is not critical for high-affinity PCNA binding.
• Flanking regions influence p21 abundance, and their N-terminal context and composition are vital for nuclear localization.

Conclusions:

• The PCNA-binding SLiM of p21 is modulated by flanking regions through charge-based interactions.
• Conserved flanking regions suggest a significant biological role beyond high-affinity binding, impacting p21 localization and abundance.
• The integration of SLiMs into composite motifs presents complexities for functional analysis and therapeutic targeting.