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Related Experiment Videos

A thermodynamic study of the trp repressor-operator interaction

J E Ladbury1, J G Wright, J M Sturtevant

  • 1Department of Chemistry, Yale University, New Haven, CT 06510.

Journal of Molecular Biology
|May 20, 1994
PubMed
Summary

The trp repressor/operator complex formation is enthalpically driven, unlike most protein/DNA interactions. This binding involves a primary strong mode and a secondary weaker mode, both showing significant negative heat capacity changes.

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Area of Science:

  • Biophysics
  • Molecular Biology
  • Thermodynamics

Background:

  • Protein-DNA interactions are crucial for gene regulation.
  • The trp repressor/operator complex is a model system for studying specific binding.
  • Heat capacity changes provide insights into the thermodynamics of complex formation.

Purpose of the Study:

  • To measure the heats of formation of the trp repressor/operator complex.
  • To investigate the thermodynamic driving forces and heat capacity changes associated with binding.
  • To understand the contribution of stereospecificity and hydration to binding thermodynamics.

Main Methods:

  • Direct titration calorimetry was used to measure heats of formation.
  • Experiments were conducted over a temperature range of 10°C to 40°C.

Related Experiment Videos

  • Analysis focused on heat capacity changes (ΔCp) and enthalpy (ΔH).

    • Main Results:

    • A primary strong binding mode was identified, exhibiting a large negative heat capacity change and being enthalpically driven.
    • A secondary, weaker "half-site" binding mode was also detected, with a similarly large negative heat capacity change.
    • The observed negative ΔCp was attributed to the stereospecific restriction of hydrated polar elements at the interface, rather than buried non-polar surfaces.

    Conclusions:

    • The trp repressor/operator complex formation is enthalpically driven across physiological temperatures.
    • Large negative heat capacity changes are linked to stereospecific interfaces and restricted water structure, not solely high affinity or buried hydrophobic surfaces.
    • The "tightening of soft internal modes" involving hydrated polar elements plays a significant role in the thermodynamics of specific protein-DNA recognition.