title: Human MSH2 binds to trinucleotide repeat DNA structures associated with neurodegenerative diseases.
abstract: The expansion of trinucleotide repeat sequences is associated with several neurodegenerative diseases. The mechanism of this expansion is unknown but may involve slipped-strand structures where adjacent rather than perfect complementary sequences of a trinucleotide repeat become paired. Here, we have studied the interaction of the human mismatch repair protein MSH2 with slipped-strand structures formed from a triplet repeat sequence in order to address the possible role of MSH2 in trinucleotide expansion. Genomic clones of the myotonic dystrophy locus containing disease-relevant lengths of (CTG)n x (CAG)n triplet repeats were examined. We have constructed two types of slipped-strand structures by annealing complementary strands of DNA containing: (i) equal numbers of trinucleotide repeats (homoduplex slipped structures or S-DNA) or (ii) different numbers of repeats (heteroduplex slipped intermediates or SI-DNA). SI-DNAs having an excess of either CTG or CAG repeats were structurally distinct and could be separated electrophoretically and studied individually. Using a band-shift assay, the MSH2 was shown to bind to both S-DNA and SI-DNA in a structure-specific manner. The affinity of MSH2 increased with the length of the repeat sequence. Furthermore, MSH2 bound preferentially to looped-out CAG repeat sequences, implicating a strand asymmetry in MSH2 recognition. Our results are consistent with the idea that MSH2 may participate in trinucleotide repeat expansion via its role in repair and/or recombination.
authors.affiliation: Center for Genome Research, Institute of Biosciences and Technology in the Texas Medical Center, Texas A&M University, Houston 77030, USA. cpearson@ibt.tamu.edu
authors.forename: C E
authors.initials: CE
authors.lastname: Pearson
authors.forename: A
authors.initials: A
authors.lastname: Ewel
authors.forename: S
authors.initials: S
authors.lastname: Acharya
authors.forename: R A
authors.initials: RA
authors.lastname: Fishel
authors.forename: R R
authors.initials: RR
authors.lastname: Sinden
mesh_terms: D001667:Binding, Competitive; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004260:DNA Repair; D004268:DNA-Binding Proteins; D006801:Humans; D051718:MutS Homolog 2 Protein; D009410:Nerve Degeneration / Q000235:genetics*; D009692:Nucleic Acid Heteroduplexes; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism*; D013379:Substrate Specificity; D018911:Trinucleotide Repeats
chemical_list: D004268:DNA-Binding Proteins; D009692:Nucleic Acid Heteroduplexes; D011518:Proto-Oncogene Proteins; D004247:DNA; C497172:MSH2 protein, human; D051718:MutS Homolog 2 Protein