Figure 2.

Measurement of changes in coupling free energies between Asp-41 and Thr-522 during the allosteric transition of GroEL. The coupling energy, ΔΔG_int, between two residues (Asp-41 and Thr-522) in the TR state relative to the TT state is given by (I) ΔΔG_int(TR-TT) = ΔG_TR-TT(wild-type) − ΣΔG_TR-TT(single mutants) + ΔG_TR-TT(double mutant). The coupling energy between the two residues in the RR state relative to the TR state is (II) ΔΔG_int(RR-TR) = ΔG_RR-TR(wild-type) − ΣΔG_RR-TR(single mutants) + ΔG_RR-TR(double mutant). The change in coupling energy during the allosteric transition of one ring may depend on the conformation of the adjacent ring. A measure of this dependence is given by ΔΔΔG_int = ΔΔG_int(RR-TR) − ΔΔG_int(TR-TT). Similar cycles may be constructed for the interaction between Glu-409 and Arg-501. Single-letter notation for amino acids is used.