Structural basis of human PCNA sliding on DNA

Area of Science:

• Molecular Biology
• Structural Biology
• Biophysics

Background:

• Sliding clamps, such as PCNA, are essential for DNA replication, encircling the genome to tether polymerases.
• The precise molecular mechanism governing how these clamps slide along DNA remains largely unknown.

Purpose of the Study:

• To elucidate the mechanism by which the human sliding clamp PCNA interacts with and slides along DNA.
• To understand how this interaction is critical for the assembly of functional DNA replication machinery.

Main Methods:

• X-ray crystallography was employed to determine the structural basis of PCNA-DNA interaction.
• Nuclear Magnetic Resonance (NMR) spectroscopy provided insights into the dynamic interactions.
• Molecular dynamics (MD) simulations were used to model the sliding mechanism at an atomic level.

Main Results:

• PCNA recognizes DNA via a specific double patch of basic residues in its ring channel, matching B-DNA's helical pitch.
• A 'cogwheel' mechanism involving transient polar interactions allows PCNA to slide while maintaining orientation.
• Mutations at the PCNA-DNA interface disrupt DNA synthesis initiation by polymerase delta.

Conclusions:

• PCNA's interaction with DNA is mediated by a specific structural motif that ensures correct clamp orientation.
• The proposed cogwheel mechanism explains the dynamic sliding of PCNA on the DNA backbone.
• A properly oriented PCNA is crucial for forming a functional replication complex with polymerase delta, highlighting its role in DNA replication fidelity.