Conserved Active Site Loop Residues of E. coli DinB and Human DNA Polymerase Kappa Govern Activity

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Cells utilize DNA repair and damage tolerance mechanisms to counteract ubiquitous DNA damage.
• Y-family DNA polymerases are specialized, evolutionarily conserved enzymes that confer DNA damage tolerance.
• E. coli has two Y-family polymerases, while humans possess four, including DNA polymerase kappa.

Purpose of the Study:

• To investigate the role of active site loops in the function of E. coli DinB and human DNA polymerase kappa.
• To compare the effects of mutations in conserved active site loop residues on enzyme activity and stability.

Main Methods:

• Alanine scanning mutagenesis was performed on the active site loops of DinB and DNA polymerase kappa.
• Primer extension assays were used to characterize the DNA damage bypass activity of the mutant polymerases.
• Thermal stability assays were conducted to assess the impact of mutations on protein stability.

Main Results:

• Most alanine substitution variants exhibited activity and stability comparable to their wild-type counterparts.
• Specific mutations in aligned residues led to significant reductions in polymerase activity and/or stability.
• The observed effects of mutations were remarkably similar between E. coli DinB and human DNA polymerase kappa.
• Less active variants generally showed reduced stabilization by DNA and incoming nucleotides.

Conclusions:

• The active site loop plays a critical role in the catalytic activity and stability of Y-family DNA polymerases.
• Conserved residues within the active site loop are crucial for the function of both DinB and DNA polymerase kappa.
• These findings highlight the conserved nature of DNA damage tolerance mechanisms across different species.