A Disease-Causing Variant in PCNA Disrupts a Promiscuous Protein Binding Site

Area of Science:

• Structural biology
• Molecular genetics
• Biochemistry

Background:

• Proliferating cell nuclear antigen (PCNA) is a crucial ring-shaped protein complex acting as a sliding platform for DNA replication.
• PCNA coordinates cellular pathways with DNA replication, ensuring genomic stability.
• A specific mutation (Ser228Ile) in human PCNA causes disease symptoms similar to DNA damage and repair disorders.

Purpose of the Study:

• To elucidate the structural consequences of the Ser228Ile mutation in human PCNA.
• To understand how this mutation affects the binding interactions of PCNA with its client proteins.
• To investigate the dynamic nature of the PCNA binding site.

Main Methods:

• X-ray crystallography to determine the structure of the disease-causing PCNA variant.
• Analysis of conformational changes in the PCNA binding pocket.
• Biochemical assays to assess binding energetics with client proteins and peptides.

Main Results:

• The Ser228Ile mutation induces a large conformational change in PCNA, significantly altering the client protein binding pocket.
• The mutation markedly affects binding energetics for some PCNA client proteins.
• The binding pocket exhibits plasticity, accommodating some ligands despite the mutation, as shown with p21(CIP1) and other partner proteins.

Conclusions:

• The disease-causing PCNA mutation selectively alters interactions with client proteins due to conformational changes.
• The PCNA binding site is dynamic and pliable, capable of conformational adjustments.
• Understanding these mutation-induced alterations provides insights into DNA metabolism and related disorders.