DNA bending and unbending by MutS govern mismatch recognition and specificity

Area of Science:

• Molecular Biology
• Genetics
• Biophysics

Background:

• DNA mismatch repair (MMR) is crucial for maintaining genomic stability.
• MutS proteins initiate MMR by recognizing DNA base-base mismatches and insertion/deletion loops.
• ATP binding induces conformational changes in MutS, but the mechanism of mismatch discrimination remains unclear.

Purpose of the Study:

• To investigate the conformational changes of MutS-DNA complexes during mismatch recognition.
• To understand how MutS discriminates between mismatched and homoduplex DNA.
• To provide a structural basis for MutS-mediated DNA mismatch repair specificity.

Main Methods:

• Atomic force microscopy (AFM) was employed to examine the conformations of specific and nonspecific MutS-DNA complexes.
• AFM allowed visualization of DNA bending and unbending in the presence of MutS.
• Results were integrated with existing biochemical and crystallographic data.

Main Results:

• MutS-DNA complexes showed a single conformation with bent DNA at homoduplex sites.
• Two distinct conformations, bent and unbent DNA, were observed at mismatch sites.
• Specific mismatch recognition by MutS leads to an unbent DNA conformation.

Conclusions:

• MutS initially binds DNA nonspecifically and bends it to scan for mismatches.
• Upon specific mismatch detection, MutS undergoes conformational changes, leading to an initial recognition complex with kinked DNA.
• The final state involves a further conformational change to an unbent DNA complex, elucidating the mechanism of MMR specificity.