Arabidopsis MutS homologs-AtMSH2, AtMSH3, AtMSH6, and a novel AtMSH7-form three distinct protein heterodimers with different specificities for mismatched DNA

Area of Science:

• Molecular Biology
• Genetics
• Plant Science

Background:

• Mismatch repair (MMR) is crucial for maintaining genomic stability in eukaryotes.
• Arabidopsis thaliana possesses MutS homologs involved in MMR, analogous to human MSH proteins.

Purpose of the Study:

• To investigate the interactions and DNA binding specificities of Arabidopsis MMR proteins, specifically focusing on the novel AtMSH7.
• To characterize the heterodimerization of Arabidopsis MSH2 with other MSH proteins (AtMSH3, AtMSH6, AtMSH7) and their DNA binding capabilities.

Main Methods:

• In vitro transcription and translation were used to produce Arabidopsis MSH proteins.
• Analytical gel filtration chromatography assessed protein-protein interactions and heterodimer formation.
• Electrophoretic mobility-shift assays (EMSAs) evaluated the binding of heterodimers to various DNA mismatch substrates.

Main Results:

• Arabidopsis AtMSH2 formed stable heterodimers with AtMSH3, AtMSH6, and AtMSH7, with no observed homodimerization.
• AtMSH2*AtMSH3 heterodimers preferentially bound insertion-deletion mismatches.
• AtMSH2*AtMSH6 showed strong binding to single nucleotide (+T) insertions and moderate binding to base/base mispairs (T/G).
• AtMSH2*AtMSH7 displayed unique specificity, with moderate affinity for (T/G) mispairs and weak binding to (+T) insertions.

Conclusions:

• Arabidopsis has distinct MutS heterodimers with specialized roles in recognizing different types of DNA mismatches.
• The novel AtMSH7 protein, in complex with AtMSH2, suggests a specialized function in plant DNA repair, potentially for specific lesion types or contexts.