Simultaneous ligand binding to intact and partially formed ATP binding sites in the hexameric termination factor Rho.

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• Macromolecular machines coordinate function via thermodynamic coupling between ligand binding sites.
• Quantifying ligand binding in complex oligomeric systems is experimentally challenging.
• Traditional biophysical methods are insufficient for studying binding in such systems.

Purpose of the Study:

• To quantify ATP binding to the hexameric E. coli Rho termination factor using native mass spectrometry.
• To investigate the binding of ATP to both hexameric and lower-order complexes of Rho.
• To provide detailed insights into the mechanism of ligand binding in complex macromolecular machines.

Main Methods:

• Native mass spectrometry was employed to measure ATP binding.
• The E. coli termination factor Rho, a hexameric helicase, was used as the model system.
• Binding events were quantified for hexameric and substoichiometric complexes.

Main Results:

• ATP binding to hexameric and lower-order Rho complexes was successfully observed and quantified.
• Super-stoichiometric ATP binding was detected, suggesting binding to partially formed sites.
• The findings offer new interpretations of existing biochemical data.

Conclusions:

• Native mass spectrometry provides a powerful tool for studying ligand binding in complex macromolecular machines.
• Understanding ATP binding dynamics is crucial for elucidating the function of machines like Rho.
• Detailed binding insights are critical for understanding how macromolecular machines utilize ligand binding energy.