Loop II of DNA polymerase beta is important for discrimination during substrate binding

Area of Science:

• Molecular Biology
• Enzymology
• Genetics

Background:

• DNA polymerase beta (pol beta) is crucial for DNA repair.
• Loop II of pol beta is a flexible, solvent-exposed region important for polymerase activity and fidelity.
• Previous studies highlighted the significance of Loop II in maintaining DNA synthesis accuracy.

Purpose of the Study:

• To investigate the role of Loop II's length and sequence in pol beta fidelity.
• To characterize the specific errors introduced by a shortened Loop II.
• To elucidate the kinetic mechanism underlying fidelity loss.

Main Methods:

• Site-directed mutagenesis to create a pol beta variant with a shortened Loop II (ENEYP).
• Assays to measure DNA polymerase activity and fidelity.
• Kinetic analyses to determine nucleotide discrimination at the dNTP binding stage.

Main Results:

• A five-amino acid shortened Loop II (ENEYP) compromises pol beta fidelity.
• The ENEYP loop induces one-base frameshift errors and A-C transversions in a specific sequence context.
• ENEYP exhibits higher misincorporation of dGTP opposite template A due to impaired ground-state binding discrimination.

Conclusions:

• Loop II of pol beta is essential for maintaining high fidelity DNA synthesis.
• Alterations in Loop II can lead to specific DNA replication errors.
• The loop influences nucleotide binding pocket accuracy, impacting substrate discrimination and overall fidelity.