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. 2021 Apr 23;118(17):e2021899118. doi: 10.1073/pnas.2021899118

Fig. 4.

Fig. 4.

Allosteric recognition of the APH2 module in the tetrahedron TET12SN. (A) ITC titrations show that the binding affinity is increased more than 10-fold when Nb28 binds the Nb302-TET12SN complex (red isotherm) compared with its binding to TET12SN alone (blue isotherm). A similar positive coupling is also observed for titrations for Nb30 binding to TET12SN alone (blue isotherm) or to the Nb282-TET12SN complex (red isotherm) as shown on lower panel. (B) Thermodynamic cycle for formation of ternary complex Nb282-Nb302-TET12SN by two possible routes, where either Nb28 or Nb30 binds first. Interaction free energies (ΔG28, ΔG30, ΔG28/30, ΔG30/28) describe the formation of the various complexes. The coupling free energy can be calculated along either path of the cycle as ΔGCOOP = ΔG30 − ΔG30/28 = ΔG28 − ΔG28/30. (C) Thermodynamics of the allosteric coupling between Nb28 and Nb30 binding to tetrahedron TET12SN. The positive cooperativity contribution is driven by a favorable enthalpic coupling. Errors were estimated from the difference between the ΔFCOOP parameters obtained for each path leading to the ternary complex.