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Multinuclear NMR studies of the trp-repressor
J N Evans1, D N Arvidson, R P Gunsalus
1Department of Biochemistry/Biophysics, Washington State University, Pullman.
Biochimica Et Biophysica Acta
|November 20, 1992
Summary
L-tryptophan binding to Escherichia coli trp-aporepressor was studied using NMR spectroscopy. This binding interaction is crucial for gene regulation and strengthens upon DNA complex formation.
Area of Science:
- Molecular Biology
- Biochemistry
- Structural Biology
Background:
- The Escherichia coli trp-aporepressor regulates tryptophan biosynthesis genes.
- Corepressor binding induces a conformational change in the aporepressor, enabling DNA binding.
Purpose of the Study:
- To investigate the solution structure of the L-tryptophan-trp-aporepressor complex.
- To elucidate the molecular interactions between L-tryptophan and the aporepressor.
Main Methods:
- Nuclear Magnetic Resonance (NMR) spectroscopy (13C and 19F) was used to study L-tryptophan binding in solution.
- Equilibrium dialysis was employed to study the binding of various tryptophan analogues.
- Heteronuclear 19F(1H)-NOE experiments provided insights into spatial proximity.
Main Results:
- Valine-58 (Val-58) is positioned within the ring current of bound L-tryptophan and near its indole 5'-position.
- The L-tryptophan carboxylate forms a hydrogen bond with a positively charged residue, likely Arginine-54 (Arg-54).
- This hydrogen bond is strengthened upon formation of the trp-repressor-DNA complex.
Conclusions:
- The study provides detailed insights into the solution-state binding of L-tryptophan to the trp-aporepressor.
- These findings support and extend previous crystallographic data on the repressor structure and function.
- The enhanced interaction upon DNA binding highlights the cooperative nature of repressor-operator complex formation.