Biochemical characterization of a cancer-associated E109K missense variant of human exonuclease 1.

Mutations in the mismatch repair (MMR) genes MSH2, MSH6, MLH1 and PMS2 are associated with Lynch Syndrome (LS), a familial predisposition to early-onset cancer of the colon and other organs. Because not all LS families carry mutations in these four genes, the search for cancer-associated mutations was extended to genes encoding other members of the mismatch repairosome. This effort identified mutations in EXO1, which encodes the sole exonuclease implicated in MMR. One of these mutations, E109K, was reported to abrogate the catalytic activity of the enzyme, yet, in the crystal structure of the EXO1/DNA complex, this glutamate is far away from both DNA and the catalytic site of the enzyme. In an attempt to elucidate the reason underlying the putative loss of function of this variant, we expressed it in Escherichia coli, and tested its activity in a series of biochemical assays. We now report that, contrary to earlier reports, and unlike the catalytic site mutant D173A, the EXO1 E109K variant resembled the wild-type (wt) enzyme on all tested substrates. In the light of our findings, we attempt here to reinterpret the results of the phenotypic characterization of a knock-in mouse carrying the E109K mutation and cells derived from it.
AuthorsStephanie Bregenhorn, Josef Jiricny
JournalNucleic acids research (Nucleic Acids Res) Vol. 42 Issue 11 Pg. 7096-103 (Jun 2014) ISSN: 1362-4962 [Electronic] England
PMID24829445 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
Copyright© The Author(s) 2014. Published by Oxford University Press on behalf of Nucleic Acids Research.
Chemical References
  • EXO1 protein, human
  • Endodeoxyribonucleases
  • Exodeoxyribonucleases
  • MutS Homolog 2 Protein
  • DNA Repair Enzymes
  • DNA Repair Enzymes (chemistry, genetics, metabolism)
  • Endodeoxyribonucleases (metabolism)
  • Exodeoxyribonucleases (chemistry, genetics, metabolism)
  • HEK293 Cells
  • Humans
  • Models, Molecular
  • MutS Homolog 2 Protein (metabolism)
  • Mutation, Missense
  • Neoplasms (genetics)

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