Human Polβ Natural Polymorphic Variants G118V and R149I Affects Substate Binding and Catalysis.

DNA polymerase β (Polβ) expression is essential for the cell's response to DNA damage that occurs during natural cellular processes. Polβ is considered the main reparative DNA polymerase, whose role is to fill the DNA gaps arising in the base excision repair pathway. Mutations in Polβ can lead to cancer, neurodegenerative diseases, or premature aging. Many single-nucleotide polymorphisms have been identified in the POLB gene, but the consequences of these polymorphisms are not always clear. It is known that some polymorphic variants in the Polβ sequence reduce the efficiency of DNA repair, thereby raising the frequency of mutations in the genome. In the current work, we studied two polymorphic variants (G118V and R149I separately) of human Polβ that affect its DNA-binding region. It was found that each amino acid substitution alters Polβ's affinity for gapped DNA. Each polymorphic variant also weakens its binding affinity for dATP. The G118V variant was found to greatly affect Polβ's ability to fill gapped DNA and slowed the catalytic rate as compared to the wild-type enzyme. Thus, these polymorphic variants seem to decrease the ability of Polβ to maintain base excision repair efficiency.