Insights into DNA polymerase δ's mechanism for accurate DNA replication

Area of Science:

• Molecular Biology
• Biochemistry
• Computational Biology

Background:

• DNA polymerase delta (pol δ) is essential for DNA replication fidelity.
• Understanding the conformational dynamics of pol δ is key to elucidating its proofreading mechanisms.

Purpose of the Study:

• To investigate the conformational changes in DNA pol δ during DNA replication.
• To identify the mechanisms by which specific mutations (R696W, A699Q) in the fingers domain reduce DNA replication fidelity.
• To explore the role of magnesium ions and the β-hairpin in DNA switching and proofreading.

Main Methods:

• All-atom molecular dynamics simulations of DNA pol δ systems.
• Analysis of conformational changes, including open and closed states.
• Investigation of the impact of metal ion coordination and mutations on enzyme activity.

Main Results:

• A distinct open conformation of pol δ exists without an incoming nucleotide, characterized by finger rotation.
• The closed conformation, stabilized by three magnesium ions, is optimal for DNA synthesis.
• Removal of a third magnesium ion triggers shifts in the enzyme, promoting DNA transfer to the exonuclease site via β-hairpin interactions.
• Mutations R696W and A699Q disrupt the open-to-closed transition and β-hairpin repositioning, leading to reduced fidelity.

Conclusions:

• The third metal ion (metal ion 'C') plays a critical role in regulating DNA primer transfer between polymerase and exonuclease active sites.
• The β-hairpin is implicated in DNA switching, with specific residues (Lys444, Tyr446) influencing proofreading.
• Mutations in the fingers domain directly impair nucleotide selectivity and increase error rates by altering conformational dynamics.