Folding and binding stability of the \textit{$\varepsilon $} and \textit{$\theta $} subunits of DNA polymerase III.

POSTER

Abstract

The \textit{$\varepsilon $} subunit of DNA polymerase III is responsible for the proofreading and repair functions of the holoenzyme during DNA replication. The \textit{$\theta $} subunit binds to the \textit{$\varepsilon $} subunit. This binding has been suggested to provide additional folding stability to the \textit{$\varepsilon $} subunit. We have studied the folding stability and the binding affinity of the two subunits at 15 \r{ }C. The midpoint of urea denaturation of the \textit{$\varepsilon $} subunit was low, at 2.4 M urea, but the slope of the unfolding free energy versus urea was high (at 2.9 kcal/mol/M). The sensitivity to urea echoes the low thermal stability. In contrast, the midpoint of urea denaturation of the \textit{$\theta $} subunit was high, at 3.8 M urea, but the slope of the unfolding free energy versus urea was low (at 1.0 kcal/mol/M). Both proteins thus showed marginal stability with respect to denaturation. Their complex exhibited much greater resistance to denaturation, with a midpoint of urea denaturation at 4.3 M.

Authors

  • Daniel Spencer

    • Institute of Molecular Biophysics, Florida State University

  • Ah Young Park

  • Nicholas E. Dixon

    • Research School of Chemistry, Australian National University

  • Huan-Xiang Zhou

    • Physics Department, Institute of Molecular Biophysics
    • Institute of Molecular Biophysics and Department of Physics, Florida State University, Tallahassee, FL 32306
    • Department of Physics and Institute of Molecular Biophysics and School of Computational Science, Florida State University, Tallahassee, FL 32306
    • Inst. of Mol. Biophys. and Dept. of Phys. Florida State Univ.
    • Institute of Molecular Biophysics, Department of Physics, Florida State University
    • Institute of Molecular Biophysics \& Department of Physics, Florida State University
    • Florida State University, Institute of Molecular Biophysics and Department of Physics