Human mismatch repair protein MSH6 contains a PWWP domain that targets double stranded DNA

Area of Science:

• Molecular biology
• DNA repair mechanisms
• Cancer genetics

Background:

• The eukaryotic mismatch repair (MMR) protein MSH6 shares similarity with bacterial MutS but has an N-terminal region (NTR) with unknown function.
• Previous studies suggested yeast MSH6 NTR acts as a tether, but the human NTR's role is unclear.

Purpose of the Study:

• To characterize the structure and function of the human MSH6 N-terminal region (NTR).
• To investigate the DNA binding properties of the human MSH6 NTR and the impact of a cancer-associated mutation.

Main Methods:

• Structural analysis of human MSH6 NTR.
• DNA binding assays for double-stranded and single-stranded DNA.
• Analysis of the S144I mutation's effect on PWWP domain stability and DNA binding.

Main Results:

• Human MSH6 NTR contains a globular PWWP domain that binds double-stranded DNA with higher affinity than single-stranded DNA.
• The PWWP domain does not show preference for mismatches or nicks.
• The S144I mutation, linked to hereditary non polyposis colorectal cancer, is located on the DNA binding surface but has minimal impact on domain stability and DNA binding in vitro.

Conclusions:

• The human MSH6 PWWP domain is a DNA-binding module with distinct properties from its yeast counterpart.
• The S144I mutation's moderate effect on DNA binding suggests other factors may contribute to MMR defects in cancer.