Dynamics of MutS-mismatched DNA complexes are predictive of their repair phenotypes

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• MutS protein identifies and initiates repair of DNA mismatches and insertion/deletion loops (IDLs) in newly replicated DNA.
• The varying repair efficiencies of different DNA errors in vivo are not fully understood.
• Understanding MutS dynamics is crucial for elucidating DNA repair signaling pathways.

Purpose of the Study:

• To investigate the DNA bending dynamics induced by Thermus aquaticus MutS on different DNA mismatches/IDLs.
• To correlate these dynamics with known repair efficiencies.
• To understand the role of specific MutS mutations (E41A) in DNA repair signaling.

Main Methods:

• Single-molecule Förster resonance energy transfer (smFRET) measurements were employed.
• DNA bending dynamics were analyzed for MutS and its E41A mutant interacting with T-bulge, GT, and CC mismatches/IDLs.
• Three distinct DNA bending states (unbent/slightly bent (U), intermediate (I), and significantly bent (B)) were identified and characterized.

Main Results:

• Kinetics of interconversion among the U, I, and B states varied significantly depending on the DNA mismatch/IDL.
• Increased stability of MutS-mismatch/IDL complexes correlated with stabilization of the U state and a reduced barrier for B to U transitions.
• MutS-E41A mutant showed altered dynamics, suggesting the importance of specific interactions (hydrogen bonding) in achieving the repair-signaling U state.

Conclusions:

• DNA bending dynamics and the kinetics of transitions between bending states are critical determinants of MutS-mediated DNA repair.
• The stability of the unbent/slightly bent (U) state and the transition from the significantly bent (B) state appear essential for initiating repair signaling.
• These findings provide a mechanistic link between DNA bending dynamics, MutS interactions, and the efficiency of downstream DNA repair pathways.