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HNPCC mutations in hMSH2 result in reduced hMSH2-hMSH6 molecular switch functions
Christopher D Heinen1, Teresa Wilson, Anthony Mazurek
1Genetics and Molecular Biology Program, Department of Microbiology and Immunology, Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Abstract:
Mutations in the human mismatch repair (MMR) gene hMSH2 have been linked to approximately 40% of hereditary nonpolyposis colorectal cancers (HNPCC). While the consequences of deletion or truncating mutations of hMSH2 would appear clear, the detailed functional defects associated with missense alterations are unknown. We have examined the effect of seven single amino acid substitutions associated with HNPCC that cover the structural subdomains of the hMSH2 protein. We show that alterations which produced a known cancer-causing phenotype affected the mismatch-dependent molecular switch function of the biologically relevant hMSH2-hMSH6 heterodimer. Our observations demonstrate that amino acid substitutions within hMSH2 that are distant from known functional regions significantly alter biochemical activity and the ability of hMSH2-hMSH6 to form a sliding clamp.
Insights
Mutations in the human mismatch repair (MMR) gene hMSH2 are linked to hereditary nonpolyposis colorectal cancer (HNPCC). Missense alterations disrupt the hMSH2-hMSH6 heterodimer
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- Mutations in the human mismatch repair (MMR) gene hMSH2 account for about 40% of hereditary nonpolyposis colorectal cancers (HNPCC).
- The functional consequences of missense mutations in hMSH2 are not well understood, unlike deletion or truncating mutations.
Purpose of the Study:
- To investigate the functional impact of specific missense alterations in the hMSH2 gene associated with HNPCC.
- To elucidate how these amino acid substitutions affect the biochemical activity and molecular function of the hMSH2 protein and its complex with hMSH6.
Main Methods:
- Examined seven single amino acid substitutions in the hMSH2 protein, chosen to represent different structural subdomains.
- Assessed the effect of these substitutions on the mismatch-dependent molecular switch function of the hMSH2-hMSH6 heterodimer.
- Evaluated the impact on the ability of the hMSH2-hMSH6 complex to form a sliding clamp.
Main Results:
- Missense alterations in hMSH2 that lead to a known cancer-causing phenotype impair the mismatch-dependent molecular switch function of the hMSH2-hMSH6 heterodimer.
- Amino acid substitutions in hMSH2, even those distant from known functional regions, significantly alter the protein's biochemical activity.
- These alterations also affect the capacity of the hMSH2-hMSH6 complex to function as a sliding clamp.
Conclusions:
- Missense mutations in hMSH2 can disrupt critical functions of the hMSH2-hMSH6 heterodimer, contributing to HNPCC.
- The study reveals that alterations in hMSH2 can have profound effects on protein function and complex formation, impacting DNA repair.
- Understanding these functional defects is crucial for diagnosing and potentially treating HNPCC associated with hMSH2 mutations.