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