Entropy plays an important role in any reaction, including protein-protein interactions. 

Binding affinity (K_a) is highly associated with enthalpy and entropy. When binding occurs, enthalpy and entropy change, leading to a change in Gibbs free energy (ΔG), which can be defined by

ΔG = ΔH - TΔS

where ΔH and ΔS are the change in enthalpy and entropy respectively and T is temperature. Decrease in enthalpy and increase in entropy leads to a small ΔG. Enthalpy, entropy and Gibbs free energy play a large role in protein-protein interactions because binding affinity is related to Gibbs free energy by the equation

K_a = e^-ΔG/RT

The smaller the ΔG, the higher the binding affinity. Therefore, a combination of small ΔH and large ΔS is required for favourable protein-protein interactions.¹

Exploring the entropic basis of protein-protein interactions can help us understand forces that drive complex formation and ultimately how the protein complex performs its function.

This virtual exhibit will focus on the entropic aspects of protein-protein interactions and demonstrate the relationship between entropy and binding affinity using several examples from the constitutive centromere associated network (CCAN) complex.

References

1. Lafont, V.; Armstrong, A. A.; Ohtaka, H.; Kiso, Y.; Amzel, L. M.; Freire, E., Compensating enthalpic and entropic changes hinder binding affinity optimization. Chemical Biology & Drug Design 2007, 69 (6), 413-422.