Functional interaction between MutL and 3'-5' exonuclease X in Escherichia coli

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Exonuclease X (ExoX) is a distributive 3'-5' exonuclease crucial for DNA recombination and repair.
• ExoX exhibits low catalytic efficiency due to its distributive nature, involving multiple binding, hydrolysis, and release cycles.
• Identifying cofactors to enhance ExoX activity is essential for understanding DNA repair mechanisms.

Purpose of the Study:

• To identify protein cofactors that can enhance the exonuclease activity of ExoX.
• To characterize the interaction between ExoX and its identified cofactor, MutL.
• To elucidate the mechanism and regulatory aspects of MutL's effect on ExoX activity.

Main Methods:

• Screening of DNA repair and recombination proteins for ExoX cofactor activity.
• Surface Plasmon Resonance (SPR) and Far-Western analysis to verify protein interactions.
• Construction and analysis of deletion mutants to map interaction domains and regulatory elements.

Main Results:

• MutL was identified as a potent promoter of ExoX exonuclease activity.
• The interaction between MutL and ExoX was confirmed using biophysical and biochemical methods.
• MutL's enhancement of ExoX activity is independent of ATP and MutL's DNA-binding capability, primarily mediated by ionic interactions with MutL's N-terminus.

Conclusions:

• MutL acts as a novel cofactor, significantly boosting ExoX's DNA excision efficiency.
• The functional interaction is primarily driven by electrostatic interactions involving the N-terminus of MutL.
• This finding suggests a new regulatory role for MutL in DNA repair pathways and hints at its potential involvement in modulating other DnaQ family exonucleases.