Single-molecule FRET TACKLE reveals highly dynamic mismatched DNA-MutS complexes

Area of Science:

• Molecular Biology
• Biophysics
• Genetics

Background:

• DNA mismatch repair (MMR) is crucial for genomic stability.
• MutS proteins initiate MMR by recognizing DNA mismatches and insertion/deletion loops (IDLs).
• Understanding the dynamic conformational changes of MutS-DNA complexes is key to elucidating MMR mechanisms.

Purpose of the Study:

• To investigate the conformational dynamics of MutS-mismatch complexes using single-molecule techniques.
• To characterize the DNA bending dynamics induced by MutS at a GT mismatch.
• To develop and apply a novel analysis method for complex dynamic biological systems.

Main Methods:

• Single-molecule fluorescence resonance energy transfer (smFRET) was employed to measure DNA bending.
• A new analysis approach, FRET TACKLE, was developed, combining FRET transition analysis with kinetic lifetime examination.
• Monte Carlo simulations were used to complement experimental data and validate findings.

Main Results:

• MutS-GT mismatch recognition complexes are highly dynamic, transitioning between multiple conformational states.
• Six distinct conformations were identified, with lifetimes varying up to 20-fold and interconversion rates varying by two orders of magnitude.
• The FRET TACKLE method successfully identified conformational states and characterized binding/conformational equilibria.

Conclusions:

• The dynamic conformational states of MutS-mismatch complexes likely influence the efficiency of DNA mismatch repair.
• The FRET TACKLE method provides a powerful tool for analyzing complex dynamics in biological systems.
• These findings offer insights into the fundamental mechanisms of DNA repair and MutS-DNA interactions.