Assembly and molecular activities of the MutS tetramer

J Biol Chem. 2003 Sep 5;278(36):34667-73. doi: 10.1074/jbc.M305513200. Epub 2003 Jun 25.


Analytical equilibrium ultracentrifugation indicates that Escherichia coli MutS exists as an equilibrating mixture of dimers and tetramers. The association constant for the dimer-to-tetramer transition is 2.1 x 10(7) M-1, indicating that the protein would consist of both dimers and tetramers at physiological concentrations. The carboxyl terminus of MutS is required for tetramer assembly because a previously described 53-amino acid carboxyl-terminal truncation (MutS800) forms a limiting species of a dimer (Obmolova, G., Ban, C., Hsieh, P., and Yang, W. (2000) Nature 407, 703-710; Lamers, M. H., Perrakis, A., Enzlin, J. H., Winterwerp, H. H., de Wind, N., and Sixma, T. K. (2000) Nature 407, 711-717). MutS800 binds a 20-base pair heteroduplex an order of magnitude more weakly than full-length MutS, and at saturating protein concentrations, the heteroduplex-bound mass observed with MutS800 is only half that observed with the full length protein, indicating that the subunit copy number of heteroduplex-bound MutS is twice that of MutS800. Analytical equilibrium ultracentrifugation using a fluorescein-tagged 20-base pair heteroduplex demonstrated that native MutS forms a tetramer on this single site-sized heteroduplex DNA. Equilibrium fluorescence experiments indicated that dimer-to-tetramer assembly promotes mismatch binding by MutS and that the tetramer can bind only a single heteroduplex molecule, implying nonequivalence of the two dimers within the tetramer. Compared with native MutS, the ability of MutS800 to promote MutL-dependent activation of MutH is substantially reduced.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenosine Triphosphatases / chemistry*
  • Bacterial Proteins*
  • Binding Sites
  • DNA / metabolism
  • DNA Repair Enzymes*
  • DNA-Binding Proteins / chemistry
  • Dimerization
  • Dose-Response Relationship, Drug
  • Endodeoxyribonucleases / chemistry
  • Escherichia coli / enzymology*
  • Escherichia coli Proteins / chemistry*
  • MutS DNA Mismatch-Binding Protein
  • Protein Structure, Tertiary
  • Spectrometry, Fluorescence
  • Surface Plasmon Resonance
  • Ultracentrifugation


  • Bacterial Proteins
  • DNA-Binding Proteins
  • Escherichia coli Proteins
  • DNA
  • Endodeoxyribonucleases
  • methyl-directed mismatch repair protein, E coli
  • Adenosine Triphosphatases
  • MutS DNA Mismatch-Binding Protein
  • MutS protein, E coli
  • DNA Repair Enzymes