Dissecting the Thermodynamics of ATP Binding to GroEL One Nucleotide at a Time.

Variable-temperature electrospray ionization (vT-ESI) native mass spectrometry (nMS) is used to determine the thermodynamics for stepwise binding of up to 14 ATP molecules to the 801 kDa GroEL tetradecamer chaperonin complex. Detailed analysis reveals strong enthalpy-entropy compensation (EEC) for the ATP binding events leading to formation of GroEL-ATP and GroEL-ATP complexes. The observed variations in EEC and stepwise free energy changes of specific ATP binding are consistent with the well-established nested cooperativity model describing GroEL-ATP interactions, , intraring positive cooperativity and inter-ring negative cooperativity (Dyachenko A.